I have been using ActiveState Komodo Edit 4.1 for a few months now, and
I have been pretty impressed. I went through the same process as yourself
looking for something good on windows. I use the free edition, I don't know
what it misses on the paid for edition, but the quality of the free version
makes a strong case for its upgrade. The free edition even has code complete
(it interprets on the fly - not bad for an editor).
I haven't tried it for Rails projects though. (Just lots of camping)
For Rails I used to use RoRED a lot.
On Windows the big Java IDEs are usually your best bet. The downside is
that you have to use a big Java IDE. RadRails used to get a lot of press,
but I have never liked the Ruby support in eclipse that it is based on. Its
probably improved a bit now, but I hear it has languished a bit despite
an early strong start.
NetBeans got long ago announced as the loser in the Java IDE wars, but
somebody forgot to tell the NetBeans team. The Ruby & Rails support in the
NB 6.0 prelease builds is getting a lot of press. I only glanced at it, but I
got an immediate sense of 'rightness' from it, I have been meaning to pursue
it since. Theres also a Ruby/Rails only version of it IIRC, where there is no
other Java/whatever support, which could give your RAM a break.
Finally, theres Ruby in STEEL, IIRC Ruby support in Visual Studio. I haven't
followed this much, but they are doing some serious features (code completion