I would recommend playing against other people, no matter your level. For that,
KGS is very good.
I don't really think studying josekis is very helpful at your level. Most of the time, just playing fundamentally sound moves will carry you much much further. If you do want to learn joseki,
http://eidogo.com might be good. As for doing Go problems, which is very useful,
http://goproblems.com has probably the most extensive database. If you do use that site though, I would highly recommend actually finding the solution using your head rather than just clicking where you think the right answer is. Also,
http://senseis.xmp.net has a great amount of general Go knowledge.
This may not seem like a lot, but I got to ~12k with nothing more than this. It should be a good start for you.