My friend told me about this one. It's pretty cool.
Keyvib is a program that gives you vibration feedback when typing things in your iPhone. It works with everything I have typed in on my phone so far. It took me a few to figure out, so I thought I would let everyone know what I had to do.
Download Keyvib from Cydia. Click on the springboard icon that it created. It will pop up saying that Keyvib has been activated and you need to restart your iPhone. I tried rebooting with Bossprefs, but for some reason this didn't work for me. So, I powered down and then powered back up.
The vibration only works when you have your phone out of silent mode and you have the Key Clicks on. So, go to settings --> Sounds and enable Keyboard Clicks and make sure your switch on the side of your phone is not turned to silent.
Then, type away in an e-mail, text message, safari, whatever you want and you should get feedback with every letter you type.
It says that this does not support 3g on the developers website, but I am running it on an iPhone 3G and so is my friend.
Also, you can try Vibrus which I tried but was unsuccesful with. It does the same thing but there is a settings screen and you can configure the vibrations.
Give it a try, let me know what you think. I think it is really amazing!