I am about to pick up a new computer today, complete with a Logitech G15 keyboard. I primarily play Team Fortress 2, though certainly not exclusively. I believe I can use Fraps to report on the frame rate of any game I'm playing. Any other cool programs I can use with my G15?
For TF2 there is a custom display that you can use to show your current class, kills, deaths, etc.
The G15 Wikipedia page has a pretty good list of supported apps and links to plugins that you may need.
Honestly? I have a G15 now and I've never used the screen in TF2. I couldn't find anything worthwhile for it other than the built-in clock module. The side keys are handy but only use 1 bank, rather than the 3 available. Nothing that couldn't be handled by an unused key on the keyboard though.
If you play WoW, or some sort of RTS/RPG that requires you to have a full in-depth overview of the game, with all the usual keyboard tricks then this is a good keyboard (my stepdad plays WoW with it and uses the key banks a lot). For casual gaming you probably won't use much of the features though (but the media keys are handy to have - not uncommon though).
If you're a night owl the 2 levels of keyboard backlighting are useful - it can be very bright but there's a dimmer mode.
As far as typing goes it's a pretty sturdy keyboard. Standard layout - and perhaps you can find a use for the G1-G6 special keys in your editor if you're a programmer. If the keyboard comes with the PC then take it, if you're paying extra you might be wasting your money for things you don't need though.
I use a program called LCD Miscellany.
This keeps an eye on my CPU temps, download/upload speeds, memory etc. and I often use the G15 media display to skip tracks and listen to music whilst playing TF2.