What are ways of disposing concentrated sulpheric acid?

I once had a barrel (55 gallons) of concd H2SO4 I didn't need (and didn't want). I solved the problem by calling the company that made the stuff in town and asked them to take it off my hands. They did, but I realize that won't work in all cases.

The easy way is to call a disposal company. That may be the most expensive way, also, but for large amounts I expect its the smartest move. For SMALL amounts (a L or so), it can be neutralized with Na2CO3 or NaHCO3. But this is not a job for amateurs/beginners/limited experienced people.