Civilization: Revolution - Same as the DS game. A fun, streamlined Civ.
Undercroft - A solid first-person, turn-based dungeon crawler.
The Secret of Monkey Island - It's Monkey Island... on a phone!
Glyder 2 - I've actually only played the first Glyder, but I really enjoyed the tilt-flying experience and I've seen this one come up in recommendation lists.
PewPew - A free shooter in the vein of Geometry Wars, it has the best implementation of 'virtual dual analogs' I've seen.
Chop-chop - surprisingly fun for a tap-based action/platformer.
Tyrian - A kickass DOS shmup ported to the iPhone.
Racing isn't really my thing, but Real Racing is widely regarded as the best on the platform.
Pretty much all of these games have a demo version, so try before you buy.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.
