What gfx card to go for does depend a little on your current system and what upgrades you have planned in the near future. In terms of value for money the Rad8500 ($100ish) are excellent for those with CPUs up to about Athlon 1.4ghz / P4 1.6ghz after which the gains from a GF4TI really start to show and they're clearly worth the extra cash. Another card with great perf that's also great value for money is the GF4TI4200 ($120ish 64MB, $140ish 128MB), faster than 8500 esp with the faster CPUs and AA enabled. If you want more, then for about $190 there are GF4TI4400 and enhanced GF4TI4200 (using longer 4400/4600 design and 3.3ns BGA RAM) which are about 10-15% faster than a standard 4200. The GF4TI4600 has really come down in price and is about 10% faster than TI4400 and comes in at about $210. The Rad9700 ($350+) is a lot faster than 4600 esp if you want maximum AA and AF, the speed isn't really needed by anything yet, the DX9 hw (it's the only card with this) is unlikely to be of use for at least another 12 months and this card will devalue pretty quickly too ... but if you want the best the Rad9700 is the clear winner and will still be very capable for a good few years.
If you can wait it out the next 6 months should see NV30 (nVidia's DX9), value NV30, Rad9500 (value 9700) and Rad9700-DDRII if not a little more. IMHO if you have a GF3 or Rad8500 there isn't much need to upgrade, if you have something less you can get these for $100, a little more for a GF4TI4200 or if you need that bit more a faster GF4TI, these will be light on your wallet, play all current games very well, devalue slowly, sell on well and then you can pick up a nice DX9 card for a great price having had a very pleasant 6 month wait. Even a GF3TI200 or Rad9000 will seem like lightning to your current GF2MX400, I'd say don't overspend now and you will reap the rerwards in only a few months time.
PS. Manu makes little diff on GF4TI cards as all tend to have almost identical perf, o/c'ability, functionality, image quality, etc. The only big exceptions are some of the 4200 cards, namely AOpen, EVGA and it seems the standard Gainward cards where they cheap out on the RAM and in some cases lower the standard clocks too. I'd avoid these manus but consider all others going mostly on price and bundle. So MSI and Leadtek are both great choices, MSI GF4TI are known to o/c slightly better while most still regard Leadtek as having the slightest edge in image quality.