With two toddlers in two cars over the last three years, we've been through a couple of car seats! I'll just largely echo what's been said already. The Snugrides are great for as long as they'll fit in there. Both of our kids napped like champs in them, too. Then we went to Boulevards, but you could do the Roundabout if your kid isn't as oversized as mine are. Currently #1 is in a SafeGuard Go booster, which is easy to install and great for travel.
#2 will be following shortly, which means we'll have a nice clean Boulevard going begging. Yours gratis if you want it, Thrice. It's pink and flowery, though, which may or may not suit depending on what you're having.