What is the best gaming keyboard under $100?

Logitech Model G15 Back Lit Wired Gaming Keyboard Tested

Good intel and proper gear are the keys to victory. With the Logitech G15 keyboard, you get both. Now you can easily discover on which server your friends are playing Battlefield 2142, be notified when your World of Warcraft battleground becomes a... read more...

I personally have always used this and have had no complaints whatsoever.

Reply · Send thanks · posted 85 days ago

SteelSeries 6Gv2 Mechanical Gaming Keyboard

The SteelSeries 6Gv2, modeled after the award winning SteelSeries 7G keyboard, is the lower priced mechanical keyboard that improves the user’s ability to obtain more actions per minute than any other keyboard on the market. The SteelSeries G Seri... read more...

All hardware, no flash. MX-Cherry black switches dont click on the way down as opposed to the MX- blues on the black widow. Letters are laser etched into the keys so they dont wear off.
Steel frame, absolutely no flex in the keyboard in any direction.
Left windows key is replaced with a 'media key' that controls volume/play/pause etc. when used with the F1 - F6 keys.

This keyboard is used by the majority of Star-Craft II pro players for its durability and simplicity.

Reply · Send thanks · posted 87 days ago

The keys really feel great, has a ton of macros, takes the perfect amount of pressure to type. A really quality keyboard, and quite a bit of bang for your buck.

Reply · Send thanks · posted 89 days ago

Razer BlackWidow (Mac version)

The Razer BlackWidow is the first mechanical gaming keyboard designed to pave the way for a whole new feel and accelerated gameplay. A full mechanical key infrastructure delivers distinctive tactile feedback, superior gaming-grade response, and un... read more...

This is what I use and I have to say I am quite fond of it. I really like mechanical keyboards because to me they have the best feel and fastest response.
Black widow offers fully programmable keys and 5 additional gaming keys.
But seriously, to me the selling point for this keyboard is the tactile keys. The action is awesome and helps prevent typos/missed keys...check it out.