If you like Google Toolbar's highlighter, but you don't want to install the add-on or the toolbar doesn't support your browser, try the Word Highlight Greasemonkey script. After performing a Google search, the script highlights the keywords and lets you quickly find their occurrences. Click on the arrows displayed next to each keyword to find the next match and use the map to visualize the distribution of the keywords.
My favorite feature is that you can use the word highlighter even when you're not searching the web. Press Ctrl+/, type the keywords and the script will highlight them.
The script can be installed in Firefox (it requires Greasemonkey), Chrome 4 Beta, Opera, Safari (it requires GreaseKit).