E.C.
There are now several good seats that will last most kids until they have the maturity and size for a belt-positioning booster. Besides the britax convertibles that have already been mentioned, there's also:
-Evenflo Triumph Advance (retail ~$129 and up) - rearfacing weight limit 35 lbs., forward facing 50 lbs.
-Graco MyRide - new - rear facing to 40 lbs., forward facing to 65 lbs., retail about $130
- First Years TrueFit - similar height and weight limits as the Britax Marathon/Boulveard/Decathlon, retails for about $180
-Sunshine Kids Radian 65/80/XT - rearfacing to 35 lbs., forward facing to 65 -80 lbs depending on model (but will generally be outgrown by height before child reaches weight limit), narrowest convertible on market so it's good if you need to be able to fit 3 seats in a row. Retails for about $200-$250
In general, you want to avoid the Cosco/Eddie Bauer/Safety First Alpha Omega "3-in-1" seats that claim to be able to last from infancy through booster, because a typical child will outgrow the 5 point harness in these seats before he/she is old enough/mature enough to use the seat as a booster (and it doesn't make a very good booster anyway because the shape/geometry of the seat doesn't position the seat belt well for most kids)
And even if your child is fairly petite on the weight charts and you think "he/she probably won't hit 40 lbs. until age 7 - do I really need a seat with a 65 lb. weight limit?" , it's still worthwhile for most folks to get a seat that has a 65 lb. or higher weight limit because these seats generally have higher *height* limits than seats with 40 lb. weight limits. '4 years and 40 lbs.' is often mentioned as the *minimum* age/weight for moving a child to a booster, but many children won't really have the size or maturity to sit properly in a booster until age 5 or 6, so investing in a seat with a higher height/weight limit now can save you from having to buy a different harnessed seat if your child outgrows a 40 lb. convertible before being ready for a booster.
Scroll down the FAQ at http://community.babycenter.com/post/a991035/faq_and_car_... for info on what to look for in a car seat, descriptions of the above seats, etc. That forum and also the forums at http://www.car-seat.org/ are EXCELLENT places to go with car safety questions, because many of the regulars are certified child-passenger safety technicians and super-knowledgeable and helpful :-)
Edited to add:
The Graco Nautilus is what is called a "Combination" seat (forward facing harnessed then belt-positioning booster), which is different from a "Convertible" seat (seat that can be used with harness either rear-facing or forward facing). It's a great seat for children who are already forward facing but not the best choice for a 1YO who would be much safer rear facing for at least another year (please keep in mind that the American Academy of Pediatrics and other child safety experts including certified child-passenger safety technicians recommend that children be kept rear-facing beyond the minimum of 1 year and 20 lbs, because rear-facing provides significantly better protection to the head/spine/neck area in the event of an accident - particularly for young toddlers for whom the head is such a large percentage of the body weight - see http://www.car-safety.org/rearface.html )
My comments on Cosco were just for the "3-in-1 seats". Although they are still safe if used properly, there are now many better seats that will give you more long-term usage for about the same price (e.g. Evenflo Triumph Advance, Graco MyRide). The Cosco Scenera and its slightly more padded/taller cousin the Safety First Avenue are both good safe budget-friendly seats, just be aware that your child may outgrow it before he or she is ready for a booster.
And while Consumer Reports often has useful info on purchasing *cars*, they aren't the best reference for car seats - see this article by a certified child passenger safety tech about why: http://www.carseatsite.com/cr.htm