UPDATE: Thank you to Rixtur for the update for iOS 6. Steps updated.
This guide is adapted from Dustin Caruso’s note on viewing source in Safari for the iPhone.
1. Visit this page using Safari on your iPad.
3. Tap + then Add Bookmark (Note, you can not bookmark a blank tab, so you must visit another web page first to do this.
4. The first text field is the Title field. Change the title to View Source. Leave the second field (the Address Field) alone and hit save.
5. Tap the Bookmarks navigation item to save the changes.
Voila. Go to any web page using Safari, tap the Bookmarks icon and hit View Source. Safari will open a page of source code in plain text in a new window.