Customizing your twitter back sounds fun. Twitter offers some backrounds to choose from but if you want to be different from the rest you can do so very easily as there are a number of sites which provide some brilliant and amazing twitter backs all for free.
Having a customized twitter background adds value to your account and gives a good impression for some one who is viewing your profile thereof increasing your followers. Customized twitter background also reflects your personality and the type of tweets you tweet, so it makes sense to choose your background wisely. If not wisely then just choose an image which is nice and different

Here are some sites where you can get free twitter backgrounds:

1.twitterbacks: http://twitterbacks.com/
2.twitter style Free and custom Twitter profile backgrounds ? TweetStyle
3.twitter gallery Twitter Backgrounds Gallery
4.Twitterbackgrounds : Free & Custom Twitter Backgrounds | Twitter Images, Layouts & Designs
5. Twitter pattern: http://twitterpatterns.com/

These sites also provide highly customized twitter backs for a price.