doctorq is right about WHDLOAD. I have an A1200 with 4 MB fast mem (GVP A1208). It does run 98% of the WHDLOAD Installed games. I tried to run OS 3.9, but I got an out of memory error with the backdrop. You need at least 6 MB of fastmem to run OS 3.9.
It was a bit slow running on an 68020 CPU, but it works.
The best card you could buy, is a Blizzard 1230 IV.
I have a Blizzard 1260 with 128 MB, but you don't need it for playing most of WHDLOAD games.
A Blizzard 1230 IV can play mp3 at low quality and surfing the internet with AGA works wel, but a little slow.