TOTP/HOTP code generator
Android (web):
FreeOTP Authenticator
Android:
FreeOTP Authenticator
iOS:
FreeOTP Authenticator
WindowsPhone:
Authenticator
BlackBerry:
2 Steps Authenticator
Java:
GoogleAuthenticatorJ2ME
PalmOS:
Google Authenticator for Palm OS
Web:
TOTP One-time Password Algorithm in Javascript