There are currently two techniques I use (most likely many more) to view page source on a regular basis on my iPad and iPhone.
The second way is to use the GoodReader application, and enter the URL of a website using the Enter URL (to download) function in the Web Downloads section of the application. After the page is downloaded and saved, select and change the name of the HTML file using the Rename button in the Manage Files section. Replace the extension of the file with .txt, and tap the blue Done button when finished renaming. Then simply tap the newly named file in the My Documents list and view the page source!
NOTE: If you need to view screen shots of these steps in action, tap the Read More.. link below this paragraph.
(To view a larger image with more detailed description tap or click its thumbnail.)