Thanks to those of you who've suggested I take a look at FingerBeat for the iPhone. This app does look like it is worth getting on my iPhone. It features:
● Low latency pads
● 8x Channel Mixer with Volume/Balance/Mute functions
● 6x Skins + User Photo using camera or own gallery.
● Built in sounds + kit templates
● Demo Function
● 16bit 44Khz Sampler using internal microphone
● 16 Banks "8 user"
● 6x Pattern blocks per kit
● Ability to use microphone* with external speaker source
* only on iPhone & iPod Touch 2nd generation.
FingerBeat at the App Stpre: