Heya,
What kind of gaming? Competitive online-footstep-listening, where sound stage and imaging are more important than actual sound? Or just a well rounded headphone for gaming casually that the focus is simply on good sound and immersion?
Also, do you already have a powerful enough soundcard or do you have an external DAC/AMP setup that is appropriate to deal with high impedance headphones (250ohm to 600ohm)?
Edit: Noted you have the HD Titanium (with a built in AMP by the way). Any headphone will run from that without much effort, so you're good to go there.
Suggestions:
Inexpensive: Panasonic HTF600 with Velour Pads (good sound stage, warm, bassy, great for immersion).
Fairly priced: Fischer Audio FA-011 (great sound stage, warm, bass capable, excellent imaging, good for FPS and immersion alike, excellent all around for gaming).
Mid-tier cost: AudioTechnica AD900 (excellent sound stage, neutral, excellent imaging, great for FPS and immersion, though not as bassy for immersion games if that matters).
Mid-tier cost: BeyerDynamic DT990 (great sound stage, bassy, good detail, good imaging, great for immersion gaming).
Mid-tier cost: AKG K701 (702, Q, etc) (excellent sound stage, neutral, excellent imaging, perfect for FPS, not as bassy for immersion).
Very best,