I've done lots of State Quarter DV hunting - and it's pretty easy to figure out where to look. Probably 99% of the known varieties involve doubling within a small area at the center of the design. To my knowledge, only the Oregon Quarter DDRs (Die 1 and Die 2) involve doubling away from the center. I've found minor varieties in at least 1/3 of the State quarter designs - including 1999 Delaware and 2008 Hawaii. I've found an equal number of interesting die clashes as well. So if you have lots to search through, I'm sure you will find something to make it worth the effort. The only down side is that most varietes found have been from the Philly mint. So if most of your quarters are from denver, your finds will be fewer and far between (but perhaps more valuable?).
Searching circulated rolls by the box, I've just about filled a roll worth of Wyoming DDRs (saddle horn). Most are just specs of doubling, but some are pretty decent.
Across many designs, I've probably got close to a roll of double earlobe varieties. Most are very minor, but I have found a few standouts... like this 2005 P MN DDO
Of everything I've found, my most interesting discovery is a 2001 P NC "Extra Hair" DDO
. It is listed by Wexler as WDDO-001.
For an online reference, James Wiles/CONECA has about the most comprehensive listing of State Quarter die varieties. Here is the link to his Variety Vista site...http://www.varietyvista.com/Split%20Image.htm
But as Bill said -- there are probably lots of undiscovered varieties out there, so don't limit yourself to checking only known varieties. You might just discover a few new ones! Good luck.