After looking at the Atlanta Logos (atllogos.com) site, which lists hundreds of Atlanta startups in different stages, I realized we can do a better job of highlighting the categories, or markets, that Atlanta has a strong base. Historically, people tend to think of Atlanta as a strong market for B2B companies, Internet security (ISS), and logistics (UPS, Delta). Here are some other categories with a strong local base of companies:
- Online marketing software
- Lead generation sites (e.g. RentWiki, Clickscape, etc)
- Vertical ecommerce sites (e.g. Case-Mate, Sylvane, etc)
- Phone technologies (e.g. Cbeyond, Vocalocity, Aretta, etc)
Oh, and Atlanta has the largest number of data centers of any metro area in the country. I encourage people to talk about these other categories, in addition to the usual suspects.
What are some other startup categories with a strong base of companies in Atlanta?
David Cummings on Startups 
I should also mention that financial services and financial transaction related companies are very prominent in Atlanta (e.g. CheckFree, Equifax, etc).
Another strong category is supply chain management software (e.g. Manhattan Associates, Servigistics, Invistics, etc.)