What you want to avoid is any of the 3-in-1 seats like th Cosco Alpha Omega, Eddie Bauer, Safety 1st 3-in-1 seat. These seats rear face, then forward face, then become a booster... jack of all trades, master of none. They are ok rear facing, ok forward facing, but are outgrown way too fast forward facing (usually around age 3) and the booster portion is awful. The booster portion of these seats have consistently failed crash tests miserably, they stink as booster seats. For the money you pay for one of these seats ,you can find a seat that will last years longer.
Here are a few great options!
Evenflo Triumph ADVANCE- $130, rear facing to 35lbs, forward to 50lbs, fits most kids rf'ing to 2/3, ff'ing to 5/6.
First Years TrueFit- $170 rear facing to 35lbs, forward to 65. Fits most kids rf'ing to 3, ff'ing to 7.
Graco MyRide 65- $150 rear facing to 40lbs, forward to 65. Fits most kids rf'ing to 4, ff'ing to 6/7.
Sunshine Kids Radian- $300 rear facing to 40/45lbs, forward facing to 60/80lbs. Fits most kids rf'ing to 4, ff'ing to 7.
Britax Marathon/Boulevard- $279 rear facing to 35lbs, forward to 65lbs. Fits most kids rf'ing to 2/3, ff'ing to 6.
All of these seats will rear face your child for a couple more years, and forward face them for years beyond that. All are great choices, perform well in crash tests, and are easy to use. I like and have used all of them over the last 7yrs of car seat usage! :)
You are right to want to keep her rear facing as long as possible. A rear facing car seat is outgrown when the child goes over the weight limit or there is less than one inch of shell above the childs head. Until then, a child can remain rear facing. Google Joels Journey and Extended Rear facing for more information .