Having mentioned Bhajis I can’t not mention Griff, the mobile music studio for Windows mobile, and which is now free (which I’ve mentioned before).
So, if you have an old Windows Mobile device knocking go can grab Griff as it and all it’s plug ins are now free.
Griff had an amazing plug in architecture which I can only wish for under iOS. It was easily way ahead of it’s time.
If you don’t have an WinMo device I can recommend a Dell Axim X51 which has always done really well for me.