How much is that House Worth? Get an appraisal online.

If you are not a real estate agent, getting good comp data is difficult unless you have a good relationship with someone (i.e. my sister is a Realtor). Yes, Zillow and CyberHomes provide good AVS (Automated Valuation Systems) data in a pinch for finding potentially good deals, but when you want to make an offer and it comes down to Brass Tacks (is that still a saying?) - then there are a couple of good services to get electronic appraisals. I have used several in the past, my favorite was FirstAMRES but they have been changing their pricing and it is less affordable than it used to be - although still worth it (this is not a time to save pennies when you could earn thousands of dollars).

A new service that has caught my eye is
Electronic Appraiser On-Line Home Valuations. This service lets you get almost instant house values online which I believe to be more accurate than when I just use Zillow. Try running a few investment properties that you own through this and see if you get the same results.