Nowadays there are 2 bang for buck cards in my opinion. The first, in the mid-range category is the 6600GT. It supports all the next-generation technologies and provides good performance at an old-gen price ($150+)
Second is the X800XL. This is a truly high end card, but is retailing at VERY good prices (around $280+)
All in all, it is up to you. Give us your budget and gaming preferences - do you play doom 3 or half life 2/counter strike?
By the way, Nvidia goes LE/XT/no mark/GT/Ultra. There is no SE series that I know of
fedz