How To Detect Installed Games On A System

I am writing a application where i need to know which games are installed on a system.I have 3 ways by which i think i can detect the games

1: Scan specific parts of registry and look for key names that match with a List of Publishers. The list is manually maintained.

2: Scan the hard disk for and do same as in step 1

3: run the program in background and check for programs in memory that use a large portion of memory(which games always do) and if they use Direct X ( Which all games do except for some) then its a game.

Now i have been thinking about it and first and second method seems to be in need of a updated database ie list of publishers to make out if a particular program is game.