I used TruGreen for a few years and had pretty good results. I began using them when we had a severe dry, hot spell and suddenly my lawn seemed to be getting overrun with crabgrass. They really helped to eradicate it. Since then I've been on annual plans with aeration, overseeding, and fertilizer.
However, last year I started looking at prices of a few other places and realized that TruGreen was really expensive. I ended up switching to using my lawn cutting crew for all of those things as well for about half the cost and so far the same results. I am thinking about using the savings to put in a sprinkler system this year.