One of the ways that I like to waste my time is by playing Tomb Raider. In particular, Tomb Raider Chronicles came with a level editor which many have put to good use. A great place to find the best levels to play can be found at mprager's web site.
In a fit of madness one day, I grew disgusted with the level loading performance under WindowsXP of the Tomb Raider Level Editor version of tomb raider. A days hacking of the binary yielded a version that loads levels nearly instantaneously :-)
After working with some folks on the forums at http://www.tr-resurrection.de/mprager/boardpower.cgi I ended up patching the european version of TRLE as well as the version that came with Tomb Raider - The Last Revelation and just for grins the version of PCTomb5.exe that comes with Tomb Raider Chronicles.
So, without further introduction, here they are:
Tomb Raider Level Editor "tomb4.exe" patched for Windows XP
Tomb Raider - The Last Revelation "tomb4.exe" patched for Windows XP
Tomb Raider Chronicles "PCTomb5.exe" patched for Windows XP