The 65,000 rule
Starting with 2005, the sample size of the American Community  Survey allows the Census Bureau to provide annual estimates for Census-defined geographies with populations of 65,000 or more. (Smaller areas will be available in the future by pooling data from multiple years.)

Note: the Current Population Survey's Annual Social and Economic Supplement released at the same time will only allow for national and state-level analysis.

Census geographies
Some of the Census geographies can be daunting at first (for example, PUMA 01804 or the "Spokane, WA--ID Urbanized Area"), but they aren't as complicated as they might seem. The following links provide help navigating the ACS data, including maps:

• Cities and counties
• Metropolitan and Micropolitan Areas
• Urban areas, school districts, and Congressional Districts
• Public Use Microdata Areas
• Statewide summaries