Edward R. Jenkins

Adds new user profile fields, including Facebook, Twitter, Google+, Deviant Art and Tumblr. These new fields can be used in your template with get_author_meta(”)
For example, to add the Google+ URL you would use get_author_meta(‘googleplus’).

Better User Profile Fields

Simple plugin that adds new user profile fields, including Facebook, Twitter, Google+, Deviant Art and Tumblr.

Jesper Johansen (jayjdk)

Twitter Profile Field is a simple WordPress plugin that gives the user a new field in the profile page to add in their Twitter username.
The pluhin also provides a shortcode which allows authors to display their, or others, Twitter usernames, optionally with a link, in posts, pages, and text widgets.

Twitter Profile Field

Adds an additional field to the user profile page where the user can enter their Twitter username.

Better User Profile Fields vs Twitter Profile Field