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The things that pass for nerdy today; this is like /. from the 1920's.

Oops, sorry, I just got a dc-dc converter in the mail to run my AMD geode SBC off a marine battery. No solder involved though, so I guess it's ok, just a crimping tool

Unless you're dead set on saving a few bucks, you're much better off getting little modules like this from a reputable source (with schematics, test results, and so on) than from fly-by-night eBay sellers. For example, here's a decent buck-boost from Pololu that fits the bill and it's that much more expensive.

If you start looking hard at some of the anonymously produced and undocumented stuff that comes from China, you'll scream. You wouldn't believe some of the rookie mistakes made in the design of (some of) those modules. Also, in some cases there are some serious compromises made to reach the lowest possible price.

The 3D printing hype is a little optimistic in ways but there is more to the notion of small scale production than 3D printing. CNC machines are very main stream in industry and the cost is well within the reach of Middle America. The cost of automation is coming down and is much more accessible than it used to be.

I would also like to see a move away from big box stores. It would be nice for a change to be able to walk into a store (camera shop, hardware store, and other more or less specialty stores) and talk to some one that knows what they are talking about.

This is my current set up:

Robot Controller:
http://www.pololu.com/catalog/product/1327

Servo Controller (if you need more than the 8 provided with that particular robot controller):
http://www.pololu.com/catalog/product/1356 - these can be hooked up to the robot controller's serial interface and daisy-chained for a maximum of ~255 servos

Servos:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXGLN4&P=7 - this one happens to be a giant scale servo for more torque

Documentation:
http://www.pololu.com/docs/0J20

This is my current set up:

Robot Controller:
http://www.pololu.com/catalog/product/1327

Servo Controller (if you need more than the 8 provided with that particular robot controller):
http://www.pololu.com/catalog/product/1356 - these can be hooked up to the robot controller's serial interface and daisy-chained for a maximum of ~255 servos

Servos:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXGLN4&P=7 - this one happens to be a giant scale servo for more torque

Documentation:
http://www.pololu.com/docs/0J20

This is my current set up:

Robot Controller:
http://www.pololu.com/catalog/product/1327

Servo Controller (if you need more than the 8 provided with that particular robot controller):
http://www.pololu.com/catalog/product/1356 - these can be hooked up to the robot controller's serial interface and daisy-chained for a maximum of ~255 servos

Servos:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXGLN4&P=7 - this one happens to be a giant scale servo for more torque

Documentation:
http://www.pololu.com/docs/0J20

The DARPA device is most certainly an improvement, but consumer IMU's are rather small nowadays too - for instance this one: http://www.pololu.com/catalog/product/1268 (just ordered one)

Smallish servos for RC are in the 1.5-8 gram range, and measured to the 1/10 gram. http://www.pololu.com/catalog/category/23
There are much smaller actuators - Plantraco MicroACT. Weight is 0.41 grams and it comes with a Nano connector. http://www.bsdmicrorc.com/index.php?productID=601
Plantraco HingeACT as used on their Butterfly. Weight 0.22 gms.
And I suspect that these are on among the heavier components of small planes. http://www.microflight.com/Micro-Butterfly-RTF-Set : Wingspan 3.5 inches (114mm) Flying Weight 2.6g
So the whole airplane is 2.6g.

It's small, fast, pre-built, can be made Arduino compatible, full source available, well documented. At $99 (but you need a $10 AVR programmer and batteries) so it's just outside of your budget. Check it out on youtube.

But I can highly recommend it - http://www.pololu.com/catalog/product/975

There are numerous kits available, best sources for choosing one would be http://www.pololu.com/ , http://www.trossenrobotics.com/ , http://www.robotshop.com/ , http://www.lynxmotion.com/ , http://www.makershed.com/ and a bunch of others. http://sparkfun.com/ and http://adafruit.com/ for more general electronics components

Cant really recommend one in particular, as it depends on what you want to do. There are several categories : 2wheel differential drive bases, legged hexapods, 4wd bases, even bipeds and robotic arms.

If you get one that is designed to be Arduino-compatible, and can take any number of Arduino expansion shields, you will have endless possibilities. I'd say easiest starting point is a complete 2WD kit with some accessory sensors. This is a nice one http://www.makershed.com/product_p/mkseeed7.htm , comes with motors and all. Just pick a "mainboard" and motor driver shield and you are good to go.

You should also consider spending a bit of cash on a good multimeter, which isn't necessary but HIGHLY recommended for troubleshooting or reverse engineering.

Better yet, get this: http://www.pololu.com/catalog/product/322
Good soldering practice, works as well as any other similarily spec'd one. (the probe things are kind of cheap though) Comes with some solder and lots of extra wire IIRC. Easy to do, just follow the steps.

I teach an intro to robotics course and use this one: http://www.pololu.com/products/pololu/0225/
It is powerful (Atmega8), complete with motor controller and LCD display and cheap ($50 complete). You can program it in C using WINAVR (free download) using any PC.

The first thing to realise there are plenty of technology related hobbyists around the world, although most are not high profile and some may be different very different demographics than yourself.

Some (hobby) groups to consider looking towards for ideas and help include: woodworkers, metalworkers (hobbyists using micromills and mini-lathes from TaigTools and Sherline, etc.), model railroads, model aircrafts (static and RC), robotics, amateur radio (ham), 2600, LUGs, and Artist Run Centres/Communities

Random list of some I use or know of:
  Make magazine http://www.makezine.com/
  Instructables http://www.instructables.com/
  ARRL http://www.arrl.org/
  http://www.sparkfun.com/ (check out their tutorials)
  http://www.fpga4fun.com/ / http://www.knjn.com/
  QRP-L http://mailman.qth.net/mailman/listinfo/qrp-l/>
  GQRP http://www.gqrp.com/
  http://www.pololu.com/ (cheap stencils laser cut, e.g. 3x4 for $32)
  http://www.diyaudio.com/
  http://www.digikey.com/ (if you're still buying electronics from Radio Shack, get these 3 catalogs now!)
  http://www.mouser.com/
  http://www.jameco.com/
  the ton of various surplus/NOS dealers online
  http://www.frontpanelexpress.com/
  http://www.seattlerobotics.org/
  http://www.chibots.org/index.php
  DorkBot
  http://eyebeam.org/production/production.php?page= tools
  MIT CBA FAB http://fab.cba.mit.edu/
  http://www.leevalley.com/
  http://www.smallparts.com/
  http://www.danssmallpartsandkits.net/
  http://www.wmberg.com/
  http://www.acklandsgrainger.com/
  http://www.grainger.com/
  http://www.onlinemetals.com/
  http://www.amqrp.com/
  http://www.princessauto.com/
  http://www.sherline.com/
  http://www.taigtools.com/

You can build something like this for any laptop. The parts would be something like a USB module like this ($20 unless you're happy just using a regular serial port), an Atmel AVR microcontroller (this ($30 for the development board which is easier to use than just the component). The accelerometer outputs a pulse with a width that varies linearly with acceleration you can just write a simple loop on the AVR (using avr-gcc) to count the pulse length and then report back via the USB (or serial port). Total cost: probably well under $100 including building an AVR programmer.

This seems like a cool, relatively cheap kit to build your own robo-dog.

One of my favorite things in grad school was the laser cutter in the mech E dept. I was happy when i found Pololu which does laser cutting for $2.50 per minute. Actually having a CAD system like this is brilliant, though.