Anyone who knows me, knows I'm kind of a nut about car seat safety. I have been known to give people car seats so that they have a safe seat for their kids. When we found out I was pregnant again, I had to research car seats again, since it had been a few years since I had an infant. Not to mention, I didn't have an infant seat any more. I spent a lot of time researching car seats. Some of the best seats out there, are made by Britax. One of my favorites is the Britax Marathon. It's basically the Rolls Royce of the car seat world. Britax is known for being one of the safest seats out there, and the Marathon doesn't disapoint. It's a convertible seat that has a 5 point harness that goes up to 65 pounds, (much higher than most other seats on the market. ) It can also be rear facing until 33 pounds, which is the safest way for small children to be in the car. The cost is higher than some other seats, but your kids can use this seat for so much longer, that I think the Marathon is worth the extra cost.
If you're looking for a new car seat that will last from the time your baby comes home from the hospital until they are in school, you should look at the Britax Marathon.