Code completion in TextWrangler
TextWrangler does not natively support code completion BUT because it is so extensively 
AppleScript-able, such capabilities can be added on. In particular, BBAutoComplete adds code completion features to TextWrangler. BBAutoComplete is free (donations accepted).

Disclosure: I have no connection to C-Command Software, but I did file a bug report that led to the release of the latest version of BBAutoComplete, and served as a volunteer beta tester. It's pretty amazing software.