I've just recently downloaded the new version of Aptana, in particular the Eclipse plugin.
Maybe I was wrong back then. Maybe they hadn't earned their cred. This is quite likely.
Just a couple of days ago, I was fetching the Rails plugin for Eclipse (RadRails) and I noticed that Aptana had acquired it (cred++). I also noticed the big fat "open source" logo (cred++).
Well, now I've chucked EditPlus (windows only!), SlickEdit (pricey! convoluted!) and even the WTP (bleh) in favor of Aptana.
They even have a debugger (works only for FX, but it's worth waiting for an IE plugin). I still prefer to debug in IE, but they're definitely going in the right direction.
One of the things I like the most is how easy it is to add "code profiles". These allow Aptana to suggest and autcomplete your functions. Example: I have jQuery and I want Aptana to suggest its methods whenever I type $().
The HTML editor is also super sweet. If you do any HTML/JS/CSS whatsoever, you're wasting your time with other tools (ok, it's arguable). I invite you to prove me wrong.