On that setup I'm tempted to recommend trying out Gentoo as you say you are not afraid of the commandline - and the install guide is very easy to follow. But you will have to spend a whole heap of time compiling stuff which isn't always as fun.
And you hand configure things - so instead of doing that...
I would go with something like Mandrake or SuSE which provide you with all the tools you need to maintain your system.. And since SuSE doesn't provide ISOs for downloading (you have to buy a boxed set or do an FTP install - good business model, hard for some people though) I would have to say Mandrake would be the best option.
But there are many fine distros out there, so shop around untill you find one that you like, and then remember to support the developers - they need to eat to.