IK Multimedia has updated SampleTank 2 for iPhone and iPad. It is intended to be a major update to their flagship virtual instrument for mobile musicians. SampleTank 2 for iOS now has over 1,900 instruments.
SampleTank 2 for iOS is a sample-based virtual instrument that gives the user access to thousands of sounds from multiple categories of acoustic, electric and electronic instruments — all on their iPad or iPhone. Load up to 8 simultaneous parts from a selection of 140 included instruments in 16 categories like piano, drums, bass, guitar, strings, keyboards, synths, organs and more. These instruments can be played in a live setting or when composing with the device interface, an external keyboard or pads controller. The new SampleTank 2 sound engine is the same as its Mac/PC software counterpart, designed to produce realism and audio quality.

I have it, but have experienced some issues with it. Sound quality is nice, an improvement, but there are some functional issues I'm not happy about. I have used it for live performances and formerly you could use two fingers to select to sounds at once, and use one tap to unload a sound. Now you have to double tap to unload a sound--this is impractical in live performance. I have emailed support at IK, but not really happy with the response as of now.