If you haven't ever visited www.halowiki.net, I recommend it.  When I first saw it months ago, it was pretty unorganized and the content was written very poorly.  Hence the beauty of a wiki: the quality of the site has improved over time through its contributions from the public.  The types of information presented on the site has also evolved over time.  It began with simple information about weapons and maps, but now includes an abundance of articles on strategies and tactics ranging from general gameplay to specific game types. 

What recently caught my attention was this article on playing defense in CTF and Assault games: http://h2wiki.halowiki.net/wiki/Defence.  It's concise and talks about some points of play that may seem obvious, but when put into practice are very effective. 

On a side note, my interest in H2 is picking up again after our last LAN party.  We're attempting to organize another game night over XBox live in the next few weeks.  If you're interested, let me know.