The Fisher Price Healthy Care Booster seat is great if you want a perminent booster on your chair that is stable and can fit an infant up to a preschooler. I like this chair a lot for my daughter who is very active and needs to have a sturdy chair that she can hang on to as she crawls on and off of the chair. It can also fold down to take for when you travel, but I find it is still pretty bulky. I would suggest the My Little Seat instead for travel purposes.
The BabySmart Cooshee Booster seat is my favorite booster for a preschooler who is able to easily get in and out of a chair, and wants a very comfortable seat. Prince Lionheart sells a similar one for about $10 cheaper; however, I think the BabySmart brand is made much better. I like that this seat does NOT slide, even on a hardwood slick chair like I have. It is super easy to clean since it has no crevices or open spaces. My son says it is very comfortable, and it can be moved easily from chair to chair, or even the floor.
*Thanks Norine for suggesting this post!