I would sand it and bondo it up, then paint the tank to look brand new, then sell it on craigslist and use the money to buy a new tank....
Just kidding, lol.. From my seat the scratch doesnt look too bad, I think I would just face that side towards the wall, lol... A new tank costs as much as a new compressor.
I think if you are not going to run that machine, you have 2 optiions that may not hurt the picket as much as others..
1 sell that one and buy a new compressor, you can get a new one..
http://www.zoro.com/ingersoll-rand-electric-air-compressor-2-stage-24-cfm-2475n75/i/G2885382/ with the 20% off coupon that will be around $1750...
OR
Buy a cheap 80 gallon and throw your pump and motor on it, and put the new pump and motor that came with it on the old tank, then sell that, I am sure there are people out there that wont be bothered by that scratch... There are plenty of 80 gals out there for $800 shipped, and with a new pump and motor on your tank you should be able to get $400, so you get a new tank for $400 and an hour of swapping parts around, not too bad...
http://www.amazon.com/dp/B005AOLB68/?tag=atomicindus08-20
http://www.homedepot.com/p/Husky-80...Stage-Electric-Air-Compressor-C801H/203187346
good luck. Home depot used to have the industrial air 5hp on sale for $1199, which was a steal, one of my guys bought one for his house, and it has a baldor motor, and nice solid pump (same as curtis), he bought a bag starter for $80 and it works great, for $1300 there was no better deal of a compressor that I have seen, BUT now its back up to $1600 on home depot.com, so a moot point...