The best deal for the money is the GeForce 4 Ti 4200 card. It will perform just a bit slower than the 4400 and 4600.
There are even a couple 4200 cards out which can be overclocked easily to close to 4600 speeds.
The best right now is supposedly the Asus V8240. Hardocp
http://www.hardocp.com just reviewed it.
I'm using an MSI GeForce 4 Ti 4200 64 MB card, which can be overclocked to close to 4600 speeds as well. This card is around $170 - $180.
Note that with any of the GeForce 4 Ti cards there is a heavy strain put on your power supply and motherboard voltage regulators. Some older boards (and unfortunately some newer ones) can't handle the load and won't work right.
If you have $400 to spend, ATI's upcoming Radeon 9700 card looks like it will put the GeForce 4 Ti 4600 to shame. It probably won't be out for another couple weeks though.