Are we talking about getting the bolts loose or getting the arms out after you do?
If we're talking bolts, leverage and a good penetrant are your friends. The longer the wrench, the better. If you don't already have one, a good electric (or air if you have an air system) impact is a sound investment.
It also helps if you can get the car up in the air good, and use a floor jack to support the axle so you can move it up and down to take some of the load off of the bushings.
And just in the interest of safety, in case you haven't already, make sure you disconnect the shocks and drop the axle down far enough to remove the coil springs. If you do manage to get one of the arms out with the coil springs still installed, very bad things are likely to happen.