Bookmarklets
These bookmarklets are to resize your browser window to several common screen sizes (for testing layouts). In IE, right click and select "Add to favourites...", in Firefox bookmark in the normal way:
Note for IE7 users - these bookmarklets don't work if you have more than one tab open. Note for everyone else, these won't work if you have disabled the ability for javascript to resize your browser window in your advanced options, Firefox users should try the Web Developer Toolbar instead.