I love Komodo by activestate. It supports MANY languages.
As your typing commands it pops up a list of possible commands you may be typing as you type it. Then once you get the command name in and open the parenthesis, it gives you help as to what arguments are needed for example, it might say this...
"eregi_replace ("string pattern", "string replacement", string);"
I consider that a huge help when learning. Allows ya to write w/o having to refer to books or anything to see what arguments go in what order.
Now to the downsides...
Takes awhile to load on older computers...
The newest version (1.2) you can only get a trial license(30 days) or pay for it.
But they will allow you to download v1.1 and get a free license for it. I use it and notice no big changes between 1.1-1.2.
http://www.activestate.com/