Best AGP card to upgrade an old system for gaming?

An age old question, and I know I am going to get a lot of ^$@# for asking but, I am looking to buy an AGP video card to upgrade my old system (my 2nd system) for gaming. I find that most of the newer games, when looking to simply play (just playing at LOW everything) can't even do that much with the hardware I have (I assume mostly due to Directx & Sharder Model not allowing me to even try - as well as other things). So I am looking for a cost-effective upgrade to allow me to continue gaming just a little bit longer...

Current System Specs:
Pentium 4 3.0GHz (HT)
2.00 gigs of OCZ RAM
ATI 9800pro 256megs (is it really that bad?)
Native Resolution = 1440x900

Now I know of a bunch of options - but of course I am looking for the best hardware for the price, I don't want to buy a $200 AGP HD3850 if it is completly bottlenecked by my system and would perform as good as a $50 2400Pro (for example) - there would just be no point...

Some of the Options I've seen:
2400PRO ~ 61$ (VisionTek)
2600XT ~ 75-150$ (PowerColor or HIS 512MB)
3450 ~ 55$ (Asus AH3450/HTP/256MB)
3650 ~ 100-110$ (Asus, Saphire, HIS, PowerColor)
3850 ~ 150$ (Saphire or HIS

Now, so I can look like a total moron, my goal would be to be able to play things like Scared 2, Diablo III (when it comes out), and Unreal Tournement III (at lowest possible graphic settings) - and hopefully some of the new stuff to come out over the next 12-24 months before I upgrade the 2nd box to something better.

So - any advice would be greatly appreciated.
Thanks,

Go for the biggest one (3850) but make sure you have a good power supply.

Hope you will get good drivers support for your card and your motherboard.