Update: This appears to be on a different port for others. As Jax pointed out you can go: Eclipse, select Help -> Help contents to get there as well :o)
I was just going into some help files of Aptana when I came across the local address for the Eclipse Help system at: http://127.0.0.1:58041/help/index.jsp
In there was a wealth of information I just didn't know was on my hard drive ... though I suppose it depends on what plug-in's you've got installed but for me I had: