If you're trying to get an idea of what your business might be worth, you should try bizbuysell.com - they claim to be the largest online marketplace.
You can sift through any of the 50,000+ business for sale listings and take a peak at would people are asking for their business, and what's included in the sale price.
It's kind of like taking a flyer from your neighbors 'For Sale' sign. You see what they are asking for their house, then make some calculations and adjustments, and then you have a rough idea what your house might be worth. (But keep in mind that just because your neighbor is asking $300,000 doesn't mean that's what they'll get, or that you would get that same price)
Here's how you use the free tool:
1) Go to the website: http://www.bizbuysell.com
2) Under 'Find a Business' scroll through the different categories and pick one (Retail, Services, Manufacturing, Construction, etc.)
3) Pick a location (city, state, etc.)
4) Enter a revenue range (i.e. $250,000 - $500,000)
I believe they also have a 'paid service' option that allows you to see actual sales prices of businesses that have sold on their site.