If you use Firefox as your web browser (and why wouldn't you?) and have not yet discovered the usefulness of the Greasemonkey extension, I've found at least one Greasemonkey script that will make it worth the download. Pagerization allows search results from Google, flickr, Yahoo, Wikipedia, YouTube, del.icio.us, digg, and other sites to be preloaded, eliminating the need to hit a "next page" button or number. It sounds simple, but for me it has quickly become an essential addition for Google and flickr browsing in particular.

Let me know in the comments if you're interested in a post about other Greasemonkey scripts that I use...