I belong to Tri Wisconsin, which is a club based around Milwaukee county. There are over 300 members, so it's a large group. It is open membership. Abilities range from absolute beginner to a couple of accomplished pros.

In no particular order, here are some of the draws for me:

1. Sponsor/race fee discounts. Our tri club is very active in seeking out local sponsors (several good bike shops, a tri shop, a few running shoe stores, an MT and a chiro), putting their logos on our jersey and getting all members a significant (10-20%) discount on goods and services. They also negotiate discounted race fees for club members for some events. My membership dues are covered each and every year by the savings from these things.

2. Cameraderie. Obviously tri is not a team sport like cycling, but it is nice to see more familiar faces at races and while out training and to get encouragement from spectators, etc.

3. Group workouts. There is something going on about 5 days a week most of the year. While not all workouts are suitable for all ability levels/distances/training plans , there are usually at least 1 or 2 every week that will benefit any given athlete.

4. We usually get some decent schwag at registration each year -- something like a tech-T (this year also a neoprene transition mat). Useful stuff--not just another bike bottle or cotton t-shirt.

Best of luck!