Doesn't seem to be many agencies listed here yet. They also offer agency website design and hosting services. Over 175,000 insurance agencies listed in all 50 states. Search by zip code or do a power search. One of the most complete listings I've seen.
Agents can create free listings.
Check this one out. Association of Online Insurance Agents Despite the lofty name, this is another online agent listing service. Paid listings only, although they fees seem pretty reasonable. Seems to have a decent number of listings. Bayon Insurance Yellow Pages Paid listings section, and a free listing section under their Insurance Resource Index.