Mailing Lists, Forums, etc. There are any number of internet resources on which wargamers can communicate with like minded people, and occasionally dispute things (surely not). Here is a selection. You will probably have to register or join to view many of them.

After Rome - a group for discussion about post-Roman Europe.

Ancmed - a  general ancient and medieval wargaming/history list set up by the SOA, although it is open to all. This is not rule system specific, although DBM gets much coverage due to popularity, and is an excellent compliment to the other rules specific lists.

Dbmlist - the main English language DBM mailing list.

DBAlist - the list for the father of all the DBx rules.

DBRlist - for the renaissance version of DBx.

DBMMlist - for Phil Barker's DBM successor.

Field of Glory - Richard Bodley Scott's post-DBx rule set published by Osprey. The new world order?

BHGS Wargaming - for wargaming news, etc. in the UK.

Shattered Lances - for the Crusades era specific rules of that name.

Armati list - for those rules.

WAB list - for Warhammer Ancient Battles.

Warmaster Ancients - for the other GW historical rule set.

TNE - a list set up to facilitate the update of DBM lists, however, much of the information is historical and could be used for any rule set.

Strategos - for Phil Sabin's rule set, published by the Society of Ancients.

WAB Forum - a forum rather than email based WAB resource.

Roman Army Talk - forum covering the Roman army and its enemies.

Fanaticus  Forum - the main DBA discussion zone.  

Flames of War - official forum for the popular WWII rules.  

Old  School Wargaming - Yahoo list for discussion of a style back in fashion.

AMW (Ancient & Medieval Wargaming) - a group for the discussion and development of Neil Thomas's "Ancient and Medieval Wargaming" rules.

There are also many other mailing lists on wargaming and historical subjects, rules, etc.. Yahoogroups is a good place to search.