DS just turned 4 and still fits in his carseat by it's safety guidelines, but we're ready to move his sister into his and move him to the next stage... booster seat. Anyone have a recommendation of one they love? Or one to avoid?
DS 5 years old
DD 2 years old
{Baby GIRL due 6.1}

Re: Car booster recommendation?
I recommend a combination high-back booster that lasts to 80-100 lbs. If he can fit into the 5-pt based on the seat requirements then use it-if not, you can use the seatbelt with the high back until your states age/weight requirements for not needing a booster seat.
There is some research out there of the benefits of a high-back to a regular booster.
We just bought a Graco Nautilus and are using it with the 5pt harness until he outgrows it, then will use it as a highback booster with seatbelt. He's only been in it a week now, so I can't really say if I love or hate it. I'm still getting use to the feel of the buckles and the tightener being a little different than his old seat, but I have no complaints. It's also a very popular and affordable seat.
Also, it appears that our DS is a month older than yours and for reference sake he's 42" but only 36lbs, one reason he's still in a 5pt.
Both my kids, 2 and 4.5, have the Britax Frontier combination booster
https://www.amazon.com/Britax-Frontier-Combination-Booster-Rushmore/dp/B0038W0JI0/ref=sr_1_1?ie=UTF8&qid=1358308478&sr=8-1&keywords=britax+frontier+85
I thought dd2 was ready for a booster at 5, and she proved me wrong in less than a week on a busy highway. She's been harnessed in a Frontier since then.