What do you have running in your menu bar? Xmarks, Dropbox, PasteBot, TimeMachine, AppleScripts, Keyboard Viewer…
Evernote, Last.fm, Google Quick Search, Adium, VMware Fusion, MagicPrefs (for Magic Mouse, AirMouse, Gmail, iStats Menus, Sharing Prefs, Battery, Airport, and clock from iStats Menus.
Source: ellenich
