Everybody's going to have a slightly different answer.
You can effectively run Windows 7 in its most bloated iteration in the stock 32GB Bootcamp default recommendation if you just need Windows for conferences that look for 32-bit MSIE and an Intel processor.
In my case, since I have a 1TB drive, I decided on 240GB for Windows, and the rest for OSX. I doubt that I'll ever really fill a 1TB drive with anything, so there's the luxury of a little extra space.
All I need is an antique terminal application that runs in 32-bit mode, MSIE for oddball conferences that look for it, and MS Office for those occasions somebody does some fancy formatting that won't show up properly in iWork. Lots of space left over for storing those pesky Windows files that people over-format. 🙂
So...this is why everybody's answer is different. Won't your games fit into 240GB or so, even with all the storage for saves?