120 or 240 MHZ HD TV
The sad part is there will always be something new and better around the corner. You have to jump in sometime or you will be waiting forever.
Sony is selling a 3D tv sometime next year. 3D is big in Europe right now. I just don't like the idea of wearing special glasses when I watch tv. Plus I don't know of any TV shows shot in 3D format now.
The advice I would give is that it depends on the application. General TV watching you'll be fine with the 120. If you watch a ton of fast paced action flicks/shows you'll notice a big difference if put side by side.
The other direction I would go (again, personally) is that I won't mess around with an LCD TV. Plasmas give you a richer color especially those that are dark. The blacks are a deeper true black instead of a faded dark gray.
If you don't care about this stuff then get what fits into your budget. I'm one that can't do that because I'll be complaining about the little stuff that many won't even notice.