You can browse a couple dozen culture tests here.
About everything you'd like to know about Almea is at Virtual Verduria; or go direct to the Almeopedia. These are also ongoing models for how you might present information about your world.
For a far future that attempts to stay within known physics, see the Incatena, the setting for my novel Against Peace and Freedom.
Forget nations, it's all about the cities. Read more about Jane Jacobs here.
For language creation, read the online Language Construction Kit or better yet, buy the book. There is now a sequel, Advanced Language Construction.
This guide to chemistry may be of use in working out tech timelines.
There's also my blog, which often covers things relevant to conworlding (which you may recall from the book is: nearly anything).
Chris Wayan creates a series of alternate Earths here and rigorously works out their climates. Interesting to see the dramatic effect of a mere changes in axes, and good practice for thinking in climate zones.
Charlie Stross's blog often dives into great s.f. analysis, such as why space colonization is unlikely and the tricky problem of how to design a society for a generation ship.
Need a smart calculator? Try Wolfram Alpha. If you have to use the same formula over and over, it's way easier than a calculator, and sometimes it can even find the formula for you— e.g. enter "distance from Alpha Centauri to Sirius".
Almeopedia uses MediaWiki software... in my opinion a greater gift to the world than Wikipedia itself. Here's instructions on installing it to create your own wiki.
If you're interested in drawing, you should follow John K Stuff, written by John Kricfalusi, creator of Ren & Stimpy. John K turns out to extremely knowledgeable and punctilious about cartooning, and many of his tips apply to more realistic drawing as well.
If you want to build in Second Life, here is the Creation Portal.
Autodesk Softimage Mod Tool is apparently dead.
Blender can be found here. Since writing the PCK I've gotten into Blender; the learning curve is steep, but once you can do what you want it's great. Watch a video tutorial or two first; then, once you're stuck (and you will be), Google "Blender" plus your problem, like "Blender how to rig a skeleton".
Here's a great free textures library. They're non-tiling but still a great place to start.