I used an app for my iPhone called Voice Synth. It takes some to get used to the control but you can customize your own voice quite nicely. Plus, it has a live talk function which actually changes your voice in real time - many other voice changers record your voice, then play it back. It's a good app, and cheap....but I found that in order to avoid feedback, I had to turn down the volume quite a bit which then resulted in people not hearing me correctly. I still might do some fine tuning, but I'm getting to the point where I've got so many electronics that it's taking me forever to get suited up.
The last few troops I have gone without and am fine without it. I keep the mic extremely close to my lips so I am able to create a raspy/whisper voice which works fine. This also allows me to keep my amp nice and loud. I use the aker 12W amp.
I have recently made my setup wireless. Originally it was wired and I had my aker cable go down my body into my side pouch. I felt that this directed my voice to the side from my hip. By going wireless, I've put my amp in my thigh pouch. This directs my voice forward. Going wireless requires a transmitter in your helmet and a receiver in your pocket.