For a Steel or aluminum frame Oil is your friend.
Pre-soaking can really help move a stuck bottom bracket.
After the soaking, putting the BB tool into the splines and tapping can help break a rusty seal.

But for real power, the vice/bb tool think is the best.

However if you don't have a vice then securing the frame in a stand with the BB placed very near the clamp is also a good way to get some stability when you're torquing out the BB.

The BB tool, a crank-bolt and a large washer should keep the BB tool from slipping out when you're using a adjustable wrench.