You can go slot-by-slot and use Wowhead to find gear upgrades. Go to the master gear list and use item filters to narrow down what you're looking for by stat, item level, and source.
Perhaps even more useful. If you start at your armory page, Blizzard has a link to each item you are wearing. From that item page, there is a link to wowhead.com and you can ask wowhead.com to find upgrades.
Unfort. i cant level till i have more time when my vacation comes soon, but hopefully www.thottbot.com has upgraded their site for cata; the site is usually up to date. ive always used it to pull up all the gear for the level i want and look at which items seem to be the easiest to obtain. Compared to the armory and other sites I find it the easiest to look up the specifics of what I need.