Yes, I use a couple of good ones and I've bought plenty of pretty poor ones so I reckon these are the best. The two I'd recommend are:
GPS Kit - A GPS tracking app that records pretty much anything you can think of, has a low power mode to save on battery life and all the tracks can be exported ready for import into other programmes like Google Earth.
iTrailMap 3D - A 3D lift map for virtually every resort out there. Allows you to see your location in 3D on the mountain in relation to the lifts. Doesn't show the runs, but that's where the 'paper' piste maps come in. The piste maps are just iphone versions of the maps you normally get. Unfortunately they dont show your location on them.