Bread knives, steak knives, hot wire cutters (beware as the fumes are toxic, or so they say), wire brushes, rotating wire brushes (clamp 'em in the chuck of your drill - I use a hand crank drill since an electric drill flings foam everywhere), Surform planes, coarse grit sandpaper, utility knives...
You can use virtually anything you can think of to cut and shape foam. The main issues are fumes if you melt the stuff and little bits of static-cling foam - on the wall, on your clothes, on the carpet, on the dog...