For the TI-82 and TI-85 the cedo program makes them excellent machines for confidence intervals, inference tests, simulations, random samples, data description, curve fitting and more. In short, the cedo program makes the 82 and 85 useable.
The 83 already does everything that the cedo program does, but the cedo program does it from a menu perspective. This makes it easier for the user to use, because the user doesn't have to remember all of the special syntax in the commands. So I recommend the cedo program for the 83 also.
I have only one discalimer though. The version of the 83 program I bought had some kind of error in the hypothesis tests for the t distribution. I have all three machines in my class, so by answer comparison, and comparing with answers in the book, were able to spot the error. I called the cedo company and they were quick to send me a replacemnt disk. So if you have or are going to use the program check for accuracy.
Some of you might be wondering about the cost. It seems a little high. But this is a site-license. Once you have purchased it you can down-load it to all of your students, this year and every future year. So if initial cost is an issue, maybe the students would be willing to chip in $5 or so to purchase all three programs.
In short, actually, in long, I highly recommend the cedo program.