The latest featured alpha version has working intelligent autocomplete. it is variable scope aware, it also checks which files you've #included so it gets all the functions and keywords from there too. each keyword in the autocomplete has a icon with the color indicating where the keyword came from (C, CPP, Arduino, AVR Libc module, or user defined) and a shape indicating what it is (type, function, statement, variable, etc)
it's as close to intellisense as i can get to at the moment without basically writing a C compiler of my own.
please try it out for me 
get it here
http://code.google.com/p/avr-project-ide/