first of all, there are the man pages that come with the system. unlike linux and many other systems, the BSD's have made great strides toward having man pages that are actually useful and up to date. just type apropos yourwordhere and it'll spit out a list of man pages related to yourword.
second, as you've seen throughout this intro, the FreeBSD handbook is filled with useful information. in fact, all the stuff produced by the FreeBSD Documentation Project is pretty good.
if you're the type that likes printed docs, check out the complete freebsd, by Greg Lehey. the author is also active on the FreeBSD mailing lists, and if you post there he may answer your questions himself. this is good, because he is damn smart.
the freebsd mailing lists are perhaps the best resource out there. see this link for some info about them. be forewarned though, RTFM before you mail any list other than freebsd-questions or freebsd-newbies. the people on these lists have a low tolerence for stupidity, and if you don't at least try to help yourself, you may get flamed hard.
if you're looking for a laugh, check out how many freebsd hackers does it take to change a light bulb.
here at rpi we have a rpi.os.freebsd newsgroup, which i have found to be quite informative, and the acm is running a freebsd help email list at this url.
we also have at least one freebsd committer on campus, so if you're really stuck you can just wander around amos eaton with a lost look on your face until dave helps you ;-) but i don't recomend that...