Here is a small UI kit including some login/signup screens for iOS. Free PSD released by Freecreative.
Freebies tagged login
Here is a set of 7 sign in screens for mobile apps. Free PSD created and released by Deividas Graužinis.
7 sign in screens for apps
Here is a login template for iOS apps. Free PSD created and released by ZamfirKim.
Login template for iOS
A simple elegant free PSD button to add to your website to allow users to login with either their facebook or twitter account.
Facebook / Twitter PSD Login Buttons
How should Batman design his login form? Free PSD.