The shorter question is: which TMs can you get multiple times?
You can buy these ones from the Celadon Dept. Store:
- Hyper Beam
- Brick Break
- Secret Power
You can buy these ones from the Celadon Game Corner (requires game coins):
- Ice Beam
- Iron Tail
- Shadow Ball
The ones from the game corner are (naturally) harder to get, but remember you can always exchange money for game coins if you want to. Anything not on this list is a one-time use, so be sure you want to use them.