If you hate clicking on "next" in Google search, but you don't want to set a higher number of results in the preferences because the page loads slowly, this Greasemonkey script might be for you (requires Greasemonkey for Firefox). It loads the next page of results as you scroll down so it gives the illusion of "infinite scrolling".
This is a Japanese script as it was created by two people from Japan. One downside of the script is that it opens search results in a new window/tab, but removing that bit of code causes weird effects.
If you want a native "infinite scrolling" in Google, try SearchMash and keep pressing the space bar to automatically fetch the next results page. Microsoft's image search is also a good implementation of the concept and probably the first major search engine that used "infinite scrolling" (at first, Windows Live Search used it for web search results as well, but the feature was removed).