Apple - 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.

Unfortunately, TextWrangler is not capable of code completion. Bare Bones Software considers TextWrangler to be the free "little brother" to BBEdit. BBEdit features code completion as well as other more advanced features, but requires a purchase after the initial trial.

http://www.barebones.com/products/bbedit/comparison.html