First, you can install Gmate form the Ubuntu Rails PPA, but I don't need or want everything it has, but here are a few things I do.
First, check out this blog post I found very helpful - he has a file attached to add the syntax highlighting necessary as well as the correct mimetype file for Rails. If you are running Ubuntu 11.10 (or any other GNOME 3 distro), you need to modify his instructions to include the path of
/usr/share/gtksourceview-2.0/language-specs/as he has listed.
Other than that his instructions are solid. I also enable line numbers, current line highlighting, the embedded terminal, set my tab to a width of 2 using spaces rather than tabs and enable automatic indentation. I also disable creating a backup copy of files before saving.