This is a short tip so I’m not gonna be long. If you want to have CAPS LOCK on iPhone / iPod Touch you have to:
1. Go to Settings, General, Keyboard and turn ON Enable Caps Lock
2. double tap the Shift Key from the iPhone / iPod Touch keyboard. The Shift Key button will became blue permanently as long the CAPS LOCK is enabled. To disable it, tap once the Shift Key.
No need for a new application :)
Cons. CAPS LOCK is being disabled when you go from letters to numbers and come back. You will have to double tap again the Shift Key if you want CAPS LOCK enabled. Kinda annoying if you have a mix of CAPS LOCK letters and numbers (e.g. a password).
Tested on version 2.2.1