Well, you said handguns, so unlike others I'll leave the 50BMG out.
Nothing too extravagant. Sig P226, or S&W 617 are two that would make the list. If it were a really big windfall I'd say a 1st generation Colt SAA, or matching numbered Luger.
Cheapshooter's rules of gun ownership #1: NEVER SELL OR TRADE ANYTHING!