I was looking for guitar stuff on Google and I stumbled across a really good free program that teaches you beginner music theory and helps with sight reading. It's got a lot of good exercises/games to help you out.

It's called "Music Theory Basics" and you can get if off Cnet
http://download.cnet.com/Music-Theory-Basics/3000-2133_4-10071071.html

Here is the description from the site:

Music Theory Basics allows you to learn the names of the notes in an easy way. This program has many added benefits, such as error checking, timing the note-reading speed. The chapters of Music Theory Basics are note reading, note writing, yes or no game (note reading), learn the piano keys, rhythmical dictation, interval dictation (unison, second, third, fourth and fifth), interval ear training (unison, second, third, fourth, and fifth), create a major scale (scales of C, D, Eb, F, G, A and Bb), melodic dictation (containing the intervals above). Theory about note reading, scales, intervals, and rhythm.