Situps and crunches work fine, but you won't see the effects of them unless you burn off the excess fat on your midsection. I have quite strong abs, but you can't see them because of abdominal fat (not tons, but I don't have a flat stomach). So if I were to exercise enough to get that layer off, you'd probably see decent abs underneath.
Also, any movement burns calories. You don't start burning more calories after
you've exercised (though your metabolism might be up, I assume). But no matter how much you tone, if you're looking to lose fat then toning won't do it. You have to do cardio. Your muscles might be toned, but excess fat will hide that, if that's more what you meant by 'tone.'
I'd suggest checking out www.self.com
. Not all their advice is great but they do have info on things you can do to tone different muscles. If you want to do cardio at home, I suggest jumping jacks, jumping rope, running up and down stairs if you can... that sort of thing.
Also, check out the "physical fitness" section of this site for ideas.