iPad owners: someone snuck a version of MAME into the app store. There is no way this will last so get it while it’s hot. Note that you’ll have to use a third party utility to actually load ROMs into the thing. Also, the ROMsets you want are for 0.37b5, not the new hotness.

iTunes download:
http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=485639079&mt=8

iExplore, the utility I’m using to move ROMs (Win/Mac/):
http://www.macroplant.com/iexplorer/