Every real estate agent offers free CMA's (Competitive/Comparative Market Analysis, a.k.a. home valuations). Most take a guess by looking at a few homes close by, some even whip your address through an on-line program to get an estimate.
The better the agent, the more work goes into it.
Brokers Guild Cherry Creek Properties Ltd. 2305 E. Arapahoe Rd. #145 Centennial, CO