Sun Studio version 12 is a free download(FREE and paid support available) -- http://developers.sun.com/sunstudio/downloads/thankyou.jsp?submit=%A0FREE+Download%A0%BB%A0.
I'm sure you have code completion and debugging support including plugin support in this IDE.
Sun Studio is available for Linux as well as Solaris.
forums : http://developers.sun.com/sunstudio/community/forums/index.jsp.
Sun Studio Linux forums : http://forum.sun.com/forum.jspa?forumID=855
I'll be eager to hear your feedback on this tool.
BR,
~A
