So, I was playing around in Mario 64 one day, using my Gameshark codes on Project 64. Since using cheat codes often glitches the game, I was able to exploit a few and mess around with others. The funniest one I found is that if you go into Look mode with the moon jump cheat on, and use the moon jump, you'll exit Look mode. However, you move around like normal but the camera still acts like you are in Look mode, so Mario's head looks really derpy and hilarious. This might also work in SM64DS, but since my Action Replay broke I can't try it.
 
   Ah, the infamous Black Room of Death. There are many ways to find it, but since I'm a n00b I only know one. This one also requires Gameshark (N64) or Action Replay (SM64DS). Basically, just go to any door where the screen fades to black, and as Mario is passing through the door moon jump. This doesn't always work.

   These are two glitches I found while playing the game. If you find anymore in Mario 64 or Mario 64 DS, post them here. 

I know a lot of glitches and tricks in Super Mario 64 that don't require cheat codes, but I'm only going to mention a couple to give other people a chance to post what they know. (Yes, I made the instructions very professional sounding )

1. The Backward Long Jump

This works in a lot of places, mainly stairs. This works best on the Endless Stairs. Just long jump backwards as fast as you can by pressing the buttons very fast repeatedly and you can go right through doors without having to open them! On the Endless stairs backward long-jumping breaks the curse that makes the stairs endless so that you don't have to beat the game with 70 stars or more.

2. Getting up steep slopes - first way

This trick is easiest with a keyboard. If you're trying to use a steep slope or hill as a shortcut, if you don't do this trick you will fail at climbing steep slopes. To get up a steep slope, just jump up onto the steep slope, then press the button you use to go forwards or up. Press it really fast repeatedly until you've successfully gotten up the slope.

3. Getting up steep slopes - second way

If you're using a controller you might have trouble doing the rapid up button push thing, so you can do this: go to the hill and jump up, then press the A and B buttons to kick. Do this repeatedly not too fast not too slow and you will be up the hill faster than the other method.

4. Mario Wings to the Sky really fast!

This trick is really difficult to do. You have to have lots of Wing Cap experience and really good flying skills to do this perfectly. Go to the island in the sky in Bob-omb Battlefield and grab the Wing Cap. Then, get in the cannon. Aim the cannon at the center of the first coin ring and blast off. Keep flying up at just the right angle and speed and you will go flying through the other coin rings in incredible fast speed.

The backwards long jump? Yeah, that glitch is weird. Mario says something like "YA-YA-YA-YA-YA-YA-YA-YA-YA-YA-HOO!" I lol so much at that one.

Yeah, nothing beats the backwards long jump(To me, anyway). I heard a "zero-star" challenge was made using just that, to complete the game with that glitch and in the shortest time. It's really tough to do, and makes quite a worthy challenge ^^