I’m no designer. OK I can put together a fairly neat looking site when I need to, but beyond the basics I’m a bit stuck. In particular, I find it hard to come up with interesting colour combinations — I tend to end up with black and white with maybe some grey thrown in if I have to.
Of course the web has an answer for everything. At its most basic, colour theory is actually consistent enough that people have created tools that will tell you what colours go well together — for example, here and here. And this site is a sort of interactive colour-for-dummies tutorial.
Finally, I really like the ColourLovers site. Rather than give you an automated tool to work out good colour combinations, users submit ‘palettes’ that are then rated by others. You can browse through these submissions to find something that suits your purpose.