Online Scientific Information Portals?

Knacklappen asks: "On August 5th, vascoda, Germany's new central access point for comprehensive scientific information, goes online. It will incorporate 23 virtual libraries and 4 scientific information networks, and offer these information for free. For the paying customer, there will also be access to electronic journals. What freely accessible scientific information portals do you use? I usually turn to the following when searching for articles: arxiv.org, AVEL, CiteSeer, dissonline.de, DOE Information Bridge, DSpace, ETD, NDLTD, OAIster, OPUS, TheO. Are there any others that you can recommend?"