It all depends a fair bit on what CPU you're currently packing and what future upgrade plans you have, as well as budget of course!
GF2 cards are certainly getting long in the tooth now, and their '2D' image quality is pretty abysmal. Generally speaking a Rad8500/LE or Rad9000/PRO are very good if they are comparable to GF3 prices, but if you want AA or to get the most out of a faster CPU (Athlon 1.4ghz / P4 1.6ghz and up) then it's worth paying the extra for a GF4TI. GF4TI cards vary little depending upon manu so image quality, stock speed, o/c'ability, features etc are all very much the same. The only exception is the rare card which uses slower RAM (higher ns or cheaper brand) or is enhanced with faster RAM, better cooling etc .. the enhanced cards are usually clearly labeled as such. So basicly don't worry about getting a specific brand of GF4TI but concentrate more on price, features (VIVO/TVout etc) and bundle. With Radeon cards it is always worth double checking as manu often makes a sizable diff in terms of perf, o/c'ability and features (eg dual display), and there's also often a diff between retail and oem versions too.
So anyway it seems to break down like this...
Under $100 Rad8500/9000 type card with 128MB - Excellent perf and 3D set for the cash with GF3 perf but better image quality, dual display, TVout, DVD playback etc. Rad9000 and Rad8500LE tend to o/c well to about Rad9000PRO and Rad8500 levels.
Under $150 GF4TI4200 pref 128MB - Excellent perf, like all GF4TI esp AA and also with great image quality, dual display and slightly improved GF3 TVout, whilst additionaly gaining great speed from every mhz your CPU can offer. Great o/c'ers 4200-128MB tend to reach 4400 speeds while 4200-64 tend to reach 4600 speeds (but better off with 128MB).
Under $200 GF4TI4400 or enhanced 4200 - Great perf although not a whole lot better than a 4200 esp once they're o/c'ed. Should still expect 4600 speeds which is very nice and prices are converging.
Under $250 GF4TI4600 - Top nVidia card not a whole lot faster than a 4400 but then they've really come down in price, just don't expect too much from o/c'ing.
Under $400 Rad9700 - Easily the fastest of all current cards esp with lots of AA and Aniso, also features full DX9 hw and should already be available for around $350.
So if you have a CPU below Athlon 1.4 or P4 1.6 and you don't plan to upgrade it in the next few months then a Rad8500/9000 type card is a very good choice. If you are above this then it's really worth investing in a GF4TI or if your budget allows the awesome Rad9700. If you can wait you could see how the new nVidia cards fair (NV28 and NV30) or if a 'budget' Rad9700 or Parhelia materialises, but as with all technological stuff you'll end up waiting for the next best thing. I'd suggest most people would be best off getting a GF4TI4200 as it doesn't really have any weaknesses, will play all current games in a good res with 2xAA and max details and should sell on well when the 'budget' next gen cards are available. I like to buy in the mid-range as they perf great, don't cost too much, devalue gradually and therefore sell on well. That's my take on it all anyway LOL!