I certainly know how hard it is to decide on seats. There are so many choices!
I would think your son would fit well in any of the seats discussed here.
With that chart I gave you, you can see how much growing room he has in many different seats. I think he owuld fit great in the Tirumph Advanced, but if you don't like how it looks, then there are more choices for you. The Britax Marathon is a great seat and right now you could get a denim one on babyuniverse.com for I think it is $249 and then they also have a form you can fill out after signing up with babytv.com to get a $50 rebate
http://www.babytv.com/. Here is the link to that Britax seat in denim
http://www.babyuniverse.com/pro/baby/95443/MarathonLATCHCarSeat-NewDenim.html
They also have the fisher price safe voyage deluxe on sale for $139 and you can get a $25 rebate on that seat. Here is that link
http://www.babyuniverse.com/pro/baby/97339/FisherPriceSafeVoyageConvertibleCarSeat-RedBlack.html
All of those seats also have free shipping. These are just some options for you that could bring down the price.
As you can see in my siggie, I have a 3yo boy in the Marathon (red!) and the FPSVD mentioned above. That seat is not quite as bright of a red as it looks. It is more of a scarlet/cranberry red.
The Radian, many people like it here. I haven't really tried it out myself, though.
There is also the Regent option, but is more pricey.
Is there something in particular you are looking for in a seat?