GExperts - (FOSS) Integrated IDE tools (Already mentioned, but well deserving of further explanation). Features most used by myself include integrated grep search (which can include use of regular expressions) with a nice UI, code navigation (ctrl-g for quick search and jump to any method in unit), custom key combinations (eg you could set ctrl-shift-B to Build-All), ascii chart for any installed system fonts,
Note: FOSS - Free Open Source Software