Some more web-based tools:

Page Size Bookmarklet
Cost: FREE!
URL: http://www.q42.nl/research/

This handy tool is a little different. It's not a regular program - it's a Javascript URL. You simply add it to your favorites and whenever you are on a web page and you want to see the total size of the web page (including the size of each component), you click on that favorite, and a little popup will appear and show you all the detailed info. This is great if you're trying to manage the size of your pages.

By the way, don't bookmark the above URL - that's just the homepage that offers the program. You need to go to http://www.q42.nl/research/ and follow their instructions. It's REALLY easy and REALLY useful.

You can find other bookmarklets at:
http://www.bookmarklets.com/tools/categor.html

Keyword Density Analyzer
Cost: FREE!
URL: http://www.keyworddensity.com/

Just go to the site, put in a URL, and it'll look at your page and show you keyword densities (if you're doing SEO work). Simple, free, and useful.

Overture Search Term Suggestion Tool
Cost: FREE!
URL: http://inventory.overture.com/d/sear...ry/suggestion/

Shows you how many searches were done last month for a particular keyword or keyphrase, as well as many other related keywords and phrases. This one doesn't require you to "validate" yourself by typing in that annoying image-code thing.