First off, let me tell you that I'm a major 4chan addict.

/mu/ has given me a lot of good music to listen to
/a/ has given me quite a few high-quality torrent links and wallpapers
/v/ is full of video game tips (well it is when I go on)
/r9k/ is a great place to rant about your day and other stuff that's on your mind
/pol/ is a great place to discuss what's on your mind about politics
Hell, even /b/ can teach you something if you go into the occasional info thread.

But, despite the stereotype that all 4chan users hate Reddit, I'm just as addicted to Reddit as I am to 4chan.

/r/atheism - despite some unsavory threads blocking up the area, it's a good place for discussions about things like the universe.
/r/dolan - if the only phrase you laugh at is "gooby pls" then this board is for you.
/r/imgoingtohellforthis - this board makes me glad that i'm not the only one who enjoys tasteless, obscene, and otherwise offensive humor.

I believe it's ok to browse both sites