Title says it all. Thanks in advance!
What do you mean by something useful?
The easiest option would be Digital Photo Professional, the free software that comes with Canon DSLR’s, if you’re wanting to convert into JPG or TIFF.
Picasa will handle CR2 RAW files, and you can save it as a JPEG. Google for Freeware RAW converter and theres various other options, depending on how old the camera the CR2 file came from was. The newer it is, the less there will be.
The beta Adobe RAW will work. Actually, the non-beta will work, but I needed the beta for my T1i.
To expound on Otara’s comment: Digital Photo Professional is a free, no-registration download from Canon’s Web site, or at least it was two months ago when I downloaded it. I actually find it surprisingly useful.
If you have a Mac, then Graphic Converter (which comes with many Macs, but I think is a free download anyway) can unsurprisingly do this. It can also do most of the drawing-type tasks you’d use Paint for on a PC.