Babies R Us has a fantastic Trade In Event going on, you can score 25% off any new Car seat, stroller, travel system, high chair, play yard, bassinet, crib, or toddler bed when you trade in an old baby care item from those categories.
I wish they were having this when we bought our carseat 3 years ago. I think I might still do this because I'm needing a second carseat for Meme's house. I'm going to go on craigslist and find one very cheap and use it as my trade in. There are guidelines and certain brands you can use go here for more details.