I have found a number of online triathlon/cycling forums and resources that I check on a semi regular basis.
Triathlon
BeginnerTriathlete Focuses more on the first timer, some good basic information, and gear reviews as well as good online training plans
SlowTwitch Focuses more on the advanced triathelete, but lots of good gear for sale in the classified section as well.
Cycling
Bikeforums One of the best cycling forums on the internet, with subforums good for just about every aspect of cycling (from road racing to classic/vintage to commuting, etc…)