YAHOO GROUPS OF NOTE
There are numerous yahoo groups that one can join, but I would recommend these three above all others.
Some other groups are very informative as well, but these are the three that I enjoy the most.
Coinzappers A group that is interested in mainly non-mainstream cleaning of ancient coins. Don't let the name fool you, the group discussion covers much more than mere electrolysis. One of the main benefits of this group is simple respect. You will not be yelled at, belittled, insulted or otherwise felt unwelcome in this group, no matter what your ideas are. I can't say this about many groups.
AncientPeddler A group that, although oftentimes goes way off the topic of ancient coins, is very friendly and quite knowledgable. Many people here love to help others out with advice and experience. This group also runs a weekly Sunday auction, where one can find a wide assortment of numismatic materials (mainly ancient, but some modern). Auctions are held here.
NumisTreasures Herb's (Nemesis Coins) little online community. Although many times there isn't much activity, if you have a question it is normally promptly answered. This is a nice, small community for the beginner. People answer in plain English, so the beginning collector can understand, and not be discouraged. Herb also offers discounts for members, and oft times will let members have advanced knowledge of new coins, or even the first crack at them.