I just tried this out in the new beta of c9.io. I think that implementation is best in class.
ctr + g a tiny input box shows up in the gutter of the open file covering the line number and showing the current line number giving the input box focus and setting the text selected so you can just start typing away. As you start typing in the box it scrolls the file to the number you just typed without you having to press enter.
When you find the right line and press enter the input box disappears and you have the cursor on the wanted line.
Another nice thing is that the input box keeps a line number history as well.
It is a bit hard to explain this in words. The best way is to just try it out in c9.io I guess.