oil pan

One of the best ways to do this is to use a wide flat blade (sometimes a wide chisel will work) and a hammer. Use the hammer to tap on the blade with it between the engine block and the gasket. Be very careful not to bend the oil pan or mar the engine block.
Sometimes you have to do this tapping at many different places around the pan to get it off.
This method works pretty much every time.

carefull, a putty knife or gasket scraper is a better tool, some oilpans are very brittle, if you need to tap it use putty knife in differant spots