I've just finished the game and want to play it again but don't really feel like playing the standard campaign again. Is there anywhere that I can download custom modules?

There are a lot of modules already created from beginner to advanced. A lot are hosted on Biowares webpage. That would be a good place to start. Be careful of To Heir Is Human if you don't have a lot of poison antidotes or protection. LOL. I walked into the gameworld and was besieged by Spiders. It is supposed to be a drow module though, so I will check it out some more.