Not as complete as "Collins Unabridged" but still good
Im not sure the exact relationship between the "Ultralingua" and "Collins" brands, but I bought this before I realized that there is in fact a "Collins" brand *unabridged* German dictionary available in the iTunes store ($34.99).
While this dictionary is certainly good, its not as complete. In particular, finding expressions is not as easy. I also miss the bookmarking feature.
One good thing about this one is the standard use of the pinch-to-zoom (something those of us with not-so-perfect eyesight always appreciate). The animation when you change translation direction is also kind of cool to watch. ;)
BarkOfDelight about
Ultralingua German-English, v1.4.3