To enable cheats, start the game using the -developer command line parameter. The easiest way to do this is to right click on your Max Payne 2 desktop shortcut and select Properties. Now in the target field, add the -developer line to the end so that it reads something like

"C:\Program Files\Rockstar Games\Max Payne 2\MaxPayne2.exe" -developer

Select 'Apply', then start the game as normal.

Now during play, press ~ to bring down the console and enter the following codes:

Nude Mona:
Like above, change the command line parameter, but this time change it to:

"C:\Program Files\Rockstar Games\Max Payne 2\MaxPayne2.exe" -developerkeys

Start the game as usual. During play, press F11 to check out some player models. Use Page Up or Page Down to scroll through, and voila, nude mona.

Thanks to Revolution readers BlaCK_CeLl, Mattias Ivarsson, nick, viperomega1, RaiDen, Erikbobo, and Terzu!