The National Credit Union Administration (NCUA) provides a search engine that allows you to search for credit unions for a particular city, region, or organization. However, this doesn't always give you all of your local credit unions. For example, the Randolph-Brooks Federal Credit Union is only listed under Universal City which is suburb of San Antonio Texas. Randolph-Brooks also has branches in Austin Texas, and many people who live in Austin are eligible to join.
Private websites have tried to fill this need. Bankrate.com offers lists of credit unions for each state organized by cities. However, this isn't any better than the NCUA website. As an example for Texas credit unions, Randolph-Brooks Federal Credit Union is listed under San Antonio. There's no mention of Austin branches.
Another private website is on the right track. CU Match UP allows you to submit basic information about yourself to its credit union search engine. The basic information is all the details that would be needed to determine membership eligibility (location, employer, organizations, etc.). It then lists the credit unions that you are eligible to join. It's a great idea. However, it failed to list many credit unions in which I would be eligible to join (two of which I'm already a member). The other problem is that it doesn't include any rate information in the list. So there's no easy way to know if your local credit union has some special (like a 5% CD).
The ideal credit union resource doesn't seem to exist. So for now, my recommendation is to bookmark this blog and check back often :-)
For more information about the advantages of credit unions, check out this previous post of mine. Also, Bankrate.com has a good article about credit union benefits and how to find one.