There are going to be a lot of 2009's hitting the Certified lots right now too, as people's leases run out. Lease vehicles are a great way to go, because people baby them to death, because they're afraid of getting charged at the end of the lease. They'll be lower miles as well.
Lexus, even though it's technically Toyota at heart, seems to just have a poor track record. I'm not entirely sure of the cause, but they don't seem to hold up as well as their mainstream counterparts.
Carmax...that's going to be iffy. They cannot certify vehicles and since they're such a huge "buffet line" of vehicles, they tend to get the lower quality techs and such too. Also, they don't have a pay plan worth a hill of moldy beans for their sales staff, so you'll basically just get pushed into a car and then will never hear from them again.
Some dealerships are shady, some are not. You have to buy from a dealership to get a Certified car and after working in sales for a while, if I don't buy new, I'll only buy certified. I've had good luck with the Honda I bought off CL last year, but I got supremely lucky in that regard.
And for the love of God, I don't care how tight your budget is or how nice the sales people are, DO NOT BUY a Kia or Hyundai. Just...don't.