Show relative file size via background bar
See e.g. how github does that at https://github.com/search?q=interface%7B%7D%7B%7D&type=Code&utf8=%E2%9C%93 (Languages part)
This is in context of file list in the upper right corner. The biggest file would be 100%, the others would be scaled.
This could be in the background of the file name.
Optionally, there could also be a humanize.Bytes() size of the file next to name.
I agree with the general idea, but I'm still thinking about a good UI and implementation that solves this well.
An idea with potential is to do the following. Instead of displaying the nearest file with a full dark blue background, and all others with a full white background, rather highlight a portion of the current file that is visible on screen.
That way, when scrolling, the relative motion would indicate how big the file is. Additionally, the size of the highlighted area would also hint at that.
This is inspired by a similar table of contents UI element that can be found here:
http://www.thedailybeast.com/articles/2011/02/23/beyond-scared-straights-real-life-controversy.html
(Scroll down and note how it affects the table of contents element in top right corner.)

Here's another idea, similar to above, but more static. Can use such partial gray background to indicate relative file size. GitHub does it to display relative sizes of results per language.
