Pathfinder has a chart lying around somewhere, which is I think identical to the 3.5 chart.
http://www.d20srd.org/srd/equipment/weapons.htm
Shortswords: 1d6 1d8 2d6 3d6 4d6
However, after a certain point, you're just adding d6's.
So greatsword goes: 2d6 3d6 4d6 6d6 8d6...
Take a look at the pattern of d6's...
Twice you increase by 1d6.
Then you increase by 2d6 twice.
I think it would next be a 4d6 increase, twice.
1d6, 1d8, 2d6, 3d6, 4d6, 6d6, 8d6, 12d6, 16d6
Next it would either be 6d6 increases(increment the changes by 2. 22d6, 28d6) or 8d6 increases (double the size of the change, 24d6, 32d6). That's 10 increases right there.
Yeah, it looks pretty absurd either way. I think after a while, you should just deal out average damage, and only roll dice when you crit. Doing otherwise would really slow down the game, especially if you don't have >forty d6. And god forbid you make multiple attacks...