General Geology
If there's place to get palaeogeographical maps then this is it! There are separate maps for each time period in geologic history, plus some data on past climate. Well worth a visit.
The USGS publication and products page, with access to their publications, store and library.
A decent geology glossary in English, German, Dutch and Norwegian.
A rich resource of links, articles, news items and a discussion board.
A decent A-Z of geology. There are a few adverts scattered around the site.
A popular geology website which is part of the About network.