For larger stuff, I prefer to use muriatic acid I get from the hardware store. You have to be careful with it (reference the "acid" part), but since it's much more powerful than vinegar, you use less and save money. If you want about the same effectiveness as vinegar, I'd go with around a 1:20 acid to water ratio at most. If you want it to work a bit quicker, go with somewhere around 1:10.
A few safety notes:
1. Always add acid to water, not the other way around.
2. Chlorine gas is released when you first add the acid. Work in a well ventilated area (preferably outside) and don't breath in the gas. It will dissipate after a few moments.
3. Although muriatic acid diluted as I've described shouldn't burn most people's skin, it will burn open cuts and eyes. It's best to wear gloves and eye protection (I'm bad about following my own advice here).
Hopefully, that didn't scare you too much. It's really not very dangerous as long as you use some caution. Vinegar is of course completely safe, and I use it for all my smaller cleaning tasks.