I use an analog version, by Raagini, and an electronic Itanpura version for the iPhone, and now also on the Ipad Itabla.
Itanpura and Itabla is available at the Itunes store, for iPhone, Ipod-touch and Ipad
Itabla on the Ipad (dont mind the trendy intro music :-)
Here is a video of the Raagini
They both sound nice.
Itanpura has more possibilities, it can play 2 tanpuras and other things, you can tweak it more, but if you use it on an Iphone you should put it in airplane-mode, to avoid ringing of your Iphone while chanting or meditating :-)
Itabla Pro on the Ipad is also very usefull for making music, as it can run in the background, while playing on any kind of keyboard or synth on the Ipad (example on video is on 2 Ipads, now you can do this on one)
Hans(uman)