5 out of 5 stars.

I could read the text in TXT file.

http://images2.wikia.nocookie.net/__cb20111117001452/mlp/es/images/d/d5/Rainbow_dash_says_so_awesome-_n1304058326372_.png
Rainbow Dash: So Awesome!

Those icons are very, very good. A (I'm insisting:) very, very good alternative for the default icons. I don't know what other (common) extension suggest, as there are not much, but uncommon especialized extensions do really exist and they would give you a lot of work. If you want some suggestions…
(I'm also describing them so you can add a pertinent picture to the graphic)

• INI: A type of TXT, but used for text configuration.
• DAT, BIN, DLL: Some types of data application extensions.
• EXE: For those applications whose don't have a own icon.
• RLI, RCU: You forgot those?
• AVI: A type of video format.
• TIFF (or TFF): A image format.
• EMF: A image format.
• MIDI: A looping instrumental-based sound format.
• TTF: A text font format.

There are some other formats that I can suggest now, but they're rare and not often found, but may come handy knowing…

• BRSTM: A looping sound format, for Wii games.
• STRM: A looping sound format, for Nintendo DS games.
• U3D: Unless you have installed Real World Thumbnails, you'll probably need an icon for U3D.

Hope that those suggestions were helping you to upgrade this set.

Note: Can you answer Annonymous' answer somewhere here, so we can all change our icons?

5 out of 5 stars.

It is possible to change the icon associated with some file types and I found some directions for such here (about 1/3 the way down page):

http://www.online-tech-tips.com/computer-tips/change-file-icon/

How to use icons:

http://www.rw-designer.com/entry/873

Very nice set of all the standard icons you could ever desire!
Love the Highlights and very clear text these icons are wonderful!
Beautiful large set! Great work!