Building Your First Cluster?

An anonymous reader asks: "I'm interested in building a DIY cluster using Linux and will be using conventional Linux software. However, the number of possible ways to do this is huge. Aside from Beowulf, there's Mosix, OpenMosix, Kerrighed, Score, OpenSSI and countless others. Therein lies the problem. There are so many ways of clustering, development seems to be in fits and starts, most won't work on recent Linux kernels and there's no obvious way to mix-and-match. What have other people used? How good are the solutions out there?"