I have been using Aptana Studio lately for my PHP projects. Created on Eclipse as the base, I actually found it pretty good to start with. It has support for other languages too such as Ruby and Python(Aptana RadRails and Aptana Pydev respectively) . Take a look at the great number of Javascript libraries that it supports as well (providing great autocomplete features).
I initially could not get Autocomplete support for Jquery after installing the add on. A little bit of digging in got it working. To enable it go to
Window->Preferences->Aptana(Right column)->Editors->Javascript->CodeAssist
You will see check boxes against all the JS libraries you have installed support for. By default they will be unselected. Check them and you are ready to GO!