Eric Rowell and Nick Dizazzo have posted a great Big-O cheat sheet. The sheet gives time and space complexity for several popular algorithms such as searching, sorting, and manipulation of data structures and graphs. One feature that I like is a graph that shows the curves for O(1), O(log(n)), O(n), O(nlog(n)), O(n2), O(2n), and O(n!). It demonstrates in a dramatic way how algorithms exhibiting these behaviors differ.
If you find yourself having to look up the complexity of algorithms occasionally, bookmark this page and have the information at your fingertips.