Pretty much every highschooler I know needs to have a TI-83 or better for their math class. You need to stand out. So, stick a cooler power button in it.
My friend's macbook pro died, and we were taking it apart, when we punched out the power button (one of those awesome metallic ones just waiting to be pushed). Incidentally, we also removed the screen which we don't think will easily work as an auxiliary display for another computer, but if anyone has any ideas, speak up.
So we decided to spice up his calculator a bit, by putting the button in so it could actually be used as a power button.
You are probably wondering how to get one of these awesome buttons without destroying your computer, turns out, they are on ebay>>>
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&Item=270274001966&Category=80034&_trkparms=algo%3DLVI%26its%3DI%26otn%3D2#ht_1600wt_1167

What you need:
1. A TI-83 +, though I am pretty sure this will work with 84's, 89's, and all the others, I just haven't done it myself
2. A cool power button, any will work (as long as its the pushbutton variety), though you have to admit, the macbook pro one is the coolest. See above for source
3. JB weld, like 3$ at ace/home depot
4. Dremel/other rotary tool, with grinding wheel attachment
5. Drill with spade bit
6. Soldering Iron + solder

The original ON button retains functionality, and we are planning to add the mac startup sound soon. These calculators are made for highschool students, and are quite hard to destroy, but this does make some irreversible changes to the casing, that might void its usability on SAT tests and the like. Our plan was to cover up the button with a big name label when that time comes.
pdf is here: http://jefe.comxa.com/TI-83-power-button-mod.pdf
shhhh

Step 1: Getting Under the Hood

First step is opening the calculator:
To do this, you will need a torx 6 driver I think, as well as a small phillips. However, I managed to open that calculator without the torx. I applied a lot of pressure with the small phillips, which apparently gave it enough friction to unscrew the torx.

In addition to the screws, there are also some tabs to be tripped, 1 at the top 2 near the sides.
Take a thin piece of metal, ie. a knife. and poke through 2 halves of the shell at the points marked on the image. 1: the middle of the top edge. 2 and 3: the side edges, below the first grip ridges
Once 2 tabs are unhooked, the third will be easy.

When all thats done, BE CAREFUL, PULL THE BACK OFF THE FRONT, WITH THE KEYS DOWN.
Otherwise you might end up in a situation as I did, with all the keys falling out, which is annoying to say the least.
You will find a foil type cover, its not critical at all, you can remove it and throw it away if you want, but it marks which way the batteries go so you might as well keep it.
All of this can be reversed, when the shell is put back on the tabs will snap into place again, and the screws can be put back in, assuming you kept them. Pay attention to the image notes below.

Step 2: Removing the Board and Locating the Power Button Pad

You will find the main board, and depending on what version of the TI-83 you have, there may or may not be a board on the back of the screen. Regardless, be careful, and remember, circuits don't break themselves, and as long as you are handling it well, it will survive quite well.
Remove the board from the keymat, and then locate the power button.

Step 3: Inserting Button and Securing It

This is the tough part. Grab your rotary tool of choice and dremel out a spot you think will fit the button. When this is done. Grab a drill, take a bit that will fit the button, ours was not the normal type bit. I'm not sure what its called(spade bit?), but it is meant for wood, and it looks like this

http://www.homefront-diy.com/ekmps/shops/diydirect/images/flat_wood_drill_bit_25mm.jpg
with a flat flange a the bottom. Anything that is the right size will work....
Just drill as perpendicular to the calculator as possible through the plastic.

When thats done, grab the dremel again, and grind around the hole, to remove burrs and obstructions. You will find the the button is not flush, but rather sunken in, so the plastic around the edge needs to be thinner. Grind it down carefully with the dremel. Near the end, take a grinding wheel attachment,
looks like this: http://www.plumbersurplus.com/images/prod/6/Dremel-541-rw-95626-161501.jpg
and use it perpendicular to the surface to flatten it out for the button.

Finally, apply liberal amounts of JB weld to the edge of the button and the hole. Make sure the power symbol is facing up, and leave it there overnight to cure.
We added some styrofoam behind the button as filler, and backing, so the button wouldn't push into the calculator, but JB weld is quite powerful...

Step 4: Finding the Pads and Testing

TI was nice enough to leave us some pads on their power button module. Depending on what version of the 83 you have, they might be in different places. Turns out, the power button is just a pushbutton switch the closes a circuit when it is depressed, so heres what you do:

The power button of choice has 2 leads like most switches, and the ON button has 2 pads, if you look closely, onto which you may solder, without actually obstructing the path of the actual button as it is depressed, thus salvaging its functionality.
(The newest revision of this calculator has a star-like button formation. It works the same way and there are two pads that work there as well.)
In case you are wondering, the way this works is when the button is pressed, its connects the circuit directly to ground, and if you look on the other side of the board, there is a giant ground pad, which could host the biggest solder globule ever, if you feel you do not have enough space on the front side.

Test before soldering:
The only things keeping the calculator working from out of its case is the power, and your ability to press the on button without the keymat (we're working on that). You'll find the battery pads on the back. They should be labeled, and if they aren't, its easy enough to trace the battery leads. Wire the batteries to these pads somehow, I used clothespins pressing on wires connected to the battery storage. Then, hold the leads of your button to the pads, then press it. If it doesn't work, check connections and try different pads until it does.

Step 5: Soldering

Solder the two leads to the tested pads, then, for extra brownie points, cover the solder in extra JB weld from the button mounting. Its good stuff, fixes everything and gives you a homey, warm feeling at the same time. or maybe thats just me. Just be careful when soldering, there's not a whole lot that can go wrong, but you know....

Step 6: Finish It

Just close the calculator back up, and you are done. Stay tuned for a tutorial on how to make it play the mac startup sound when the button is pressed, adding extra cool points to your already awesome calculator.