I’m working on the 30 day trial and don’t have a lot of time to customize themes.  Is there a generic theme that works fairly well across the site and modules (forums, wiki, etc)?

EE itself has some default themes—in my opinion, they look pretty good.  You may also want to check out the Template Library—they have some nice ones there.

Hi, xiola—welcome to the forums!  Vanceone has already pointed you to our template library.  From memory, I believe The Linguist released a forum theme for Logical Blocks; but I am not sure about a wiki theme.  Most people that do customize tend to use their own designs throughout the site, and I can’t recall seeing a full collection released.

That said, you can certainly use the demo to look and do some quick customizations on the forums, at least.  That will give you a feel for how they work and then you can take your time customizing them if you decide to go ahead with ExpressionEngine.