I am in the process of enjoying a 4 pack of Green Flash's 'Palate Wrecker' imperial IPA and all I can say is WOW! This stuff packs a wallop. 9.5% ABV, and an incredible 100+ IBUs. Not for the faint of heart or the first-time IPA drinker. The quality, taste, power, and aggressive hoppiness is as good as anything out there (including Bell's Hopslam).
Palate Wrecker has over 6lbs of hops per barrel which include Centennial, Columbus, and Simcoe (TM) varieties. Its an overpowering pungeant, dank, deep leafy green brew. Not much on the citrus-y grapefruit-y side, just a kick-your-ass hoppy overload.
Last Summer I tried Green Flash's West Coast IPA and was also thoroughly impressed with its 5 hop combo of Simcoe (TM), Columbus, Centennial, Cascade, and Citra hops. That one was great too and had more of that citrus feel to it.
Green Flash's brews and most of the other Cali IPAs out there are really must-tries for the IPA lover. Some of my favorite IPAs are: (in no particular order)
Ballast Point's 'Big Eye' IPA (Cali)
Founder's 'Centennial' IPA (-Ichigan or PA) can't remember
Great Divide 'Titan' IPA (Colorado)
Bell's 'Two Hearted Ale' and 'Hopslam' (-Ichigan)
CBC's 'Columbus' IPA (Ohio)
New Belgium 'Ranger' IPA (Colorado)
Dogfishhead '60 Min/ 90 Min' IPA (Delaware)
I've yet to try:
Fathead's 'Headhunter' IPA (Ohio)
Deschute's new seasonal 'Fresh Squeezed' IPA (Oregon)