I usually tip 20-25% and a minimum of $2.00. I know that a lot of people are feeding their families with those tips. I also figure someone has to make up for those who either can't afford to tip (which is why it's important to keep the price of meals down) and for those who are too cheap to tip.
I always tip under the rule espoused by Vinnie (Steve Martin) in the movie "My Blue Heaven". "Remember, its not how much you tip, its how my you over tip."
I generally tip most service providers (except for fast food places), the barber, the cleaner, etc. I have found that the few bucks I've tipped, that probably would have ended up behind the couch cushions, generally assure that I get treated like royalty the next time I am in their establishment.