Background processes and memory usage

While monitoring my memory usage today, I noticed that that almost an entire gig of my memory was being used when I only had one or two light programs running (MacMail, iChat). Upon checking the activity monitor, I saw that there were quite a few processes running that I did not recognize and that were using quite a bit of memory. Can anyone point me to a resource that could define some of the basic processes that typically run in OS X so that I can begin the task of sorting out which ones I should have running vs which ones could be a problem. I am fairly new to the internal workings of OS X. Any help or advice that people have would be greatly appreciated.