Czuch Czuckers: The first extension I install is the All-In-One-Sidebar, which gives you an opera-like sidebar where you can put not only history and bookmarks, but everything which is or might be accessible with a toolbar-icon, and load the content in this side panel. Then I install the Web Developer Extension, Forecast Fox, del.icio.us and AdBlock Plus.

Edit: And the wonderful Download Statusbar!