I use UltraEdit, EditPlus, Notepad++, and Notepad2. All are light weight. UltraEdit does do code completion I think... I'm not really sure as I don't use it.
UltraEdit is my main editor.
EditPlus used to be my main editor (I keep it around for regex search/replace when UltraEdit's regex support doesn't work right).
Notepad2 I have associated with most code file types (php, js, css, etc) for quick editing while browsing files in Windows Explorer.
Notepad++ I use for quick editing, similar to the way I use Notepad2, but I switch to Notepad++ if I need to open up multiple files from the same project. Yeah, I should probably just open them in UltraEdit if I'm gonna do that, but for some reason I don't.
Just the way I work. I'm weird I guess?