Well, I work for ActiveState, and designed and developed most of the
Ruby support in Komodo, so I'm biased.  But I think it's what you're
looking for.

Out of the box, you get:
- autocomplete on non-binary modules (binary modules will happen...)
- Ruby-aware auto-indent, including automatic insertion of "end"s
- full-featured debugger
- class browser
- highlighting of syntax errors
- configurable syntax-based colorizing
- powerful macro language

Please excuse the blatant commercial message.

- Eric Promislow  -- ericp / activestate.com