I register .biz names that a typical small business might use, such as windowcleaning.biz. Most Fortune 500 companies wouldn't be caught dead with a .biz domain because they don't want to be seen as third rate in their market which is the world. Many small business people would find a short .biz as desirable as a long .com. They also know they are one of many thousands who do what they do, and a good keyword domain in any common extension is not going to hurt them. Chances are, the .com is owned by a big company, a speculator that want way more than their budget, or another company doing the same business in a different way or different geographic market.
I look for .biz name that fit the above profile, and normally expect to get pricing in their budget range. I figure a domain is worth what they would pay for a 1/4 page yellow pages ad in a major market, which would be in the low $XXXX to mid $XXXX range, and I normally ask in the mid $XXX range. Some examples of the type I've registered or bought are:
exterminating.biz, videoproductions.biz, jobplacement.biz, toolrepair.biz, cargotrailer.biz, digitalcopier.biz,wrecker.biz, baitshop.biz, bassboat.biz, etc.
If it doesn't relate to business, pass on it.