I have discovered two online methods for accessing tumblr, and one app for the iPad.
Tumbex has some nice features in that it shows full screen images with next/last pointers for easily clicking onto the next photo in full screen.
I prefer the screen layout for TumblViewer – all images one one endless scrollable page. It also allows one click full screen images, but no next/last pointers. One advantage of this site is it allows reposting the post to your own tumblr blog, requiring a login though.