Biorhythm Chart Maker by Louis F. Sander - With this program, you can create and print a biorhythm chart for any 38-day period, based on your date of birth.  There is additional information in the program that tells you about the three types of data on your chart.

Disk Commands by John Sisson is a part of the Commodore Educational series of programs.  This particular program is about learning the commands for the 4040 Disk System using DOS 2.0 and BASIC 4.0 on a PET, 8032 or C64.

Electronics Construction Kit is a super cool utility for creating electronic circuits on a Commodore 64.  Initially I found this program on an Italian disk magazine called Commodisk (Issue 35), but while doing some research, I found a really nice webpage over at the Dump Club 64 website that has additional screenshots and a tad more information.  I recommend you check out their site because it has a lot of great information and downloads.

Fisher Price - My Grand Piano is a music education program for ages 3 - 8 for the Commodore 64 or 128 (in C64 mode).  From what I could gather, I believe a hardware keyboard overlay accompanied this, but isn't necessary to use the software.

This is a cute educational game for kids to help them with pattern recognition.  There are various pictures that are displayed for a short amount of time then re-displayed with something missing in the picture you have to identify.  

This astronomy program, designed for persons ages 12 and up, was released in 1984 and included a 138-page manual. It provided an interactive guided tour of the universe—in the past, present, and future. The universe model could show the location of more than 1,200 stars, 88 constellations, 8 planets, deep sky objects, and the (then) future appearance (1986) of Halley’s comet. The program had four basic modes: map, set, sky, and chart. Map was used to select the location on Earth; month, day, year, and time were determined in set; optional displays were chosen in sky; and chart was used to project the sky on a celestial sphere with coordinate lines for creating, viewing, and printing your own star charts.

Here's are some links to the manual (including cheat sheet and easter eggs) and the addendum.  Additionally, here is a link to an article in the June / July issue of TPUG reviewing the Sky Travel program.

Speed Reader by Green Valley Publishing for the Commodore 64 is a tool for helping you learn to read faster.

Story Machine by Spinnaker (1982,83) - So I ran across this CRT image for the Commodore 64 and thought it might be a word processor, but after loading it, it quickly became apparent that it's a children's game that let's you create your own story in a semi-guided way.  After looking at a few screens, it struck me that it was a really neat idea, and that even young children of this day and age might find this not only fun, but educational.

Weights & Measures by Charlie Brown (Updated for the Commodore 64 by Donna W. Woody) - This is a really handy tool!  Here's a short description taken from the first part of the documentation which is in the archive:

This program will replace a whole reference library on weights and measures. Menu driven and easy to use, it allows you to convert between any two weights, volumes, lengths, areas, or rates.

Do you want to know how many teaspoons are in a gallon? Now your C-64 can tell you in a flash--- every weight and measure you can think of is included in the table. WEIGHTS & MEASURES is an invaluable tool for dealing with those "important to know, but hard to remember" conversions. But some of the conversions aren't used that much anymore--- you may have to get out a dictionary to find out what some of them are!