Put them in a bowl . Just nick the tops where they come off the vine with a sharp kife .Pour boiling water over them .Leave them for a few minutes then put them in some cold water .The skins will then peel off easily .
i cut a little cross in the bottom of the tomato, then cover in boiling water as JCL53. I used to then plunge tem into cold water. Nowadays I'm too lazy amd just wait until the water is cool enough to pick them out. The skin comes off just as easily.
As ethandron say, it can make them a bit soggy but still firm enough to de-seed and chop. If you're cooking with them anyway, it shouldn't matter.
Another more fiddly way is to make a cross at the base of the tomato and with a good sharp peeler, peel the skin off trying to keep it in tact. Then roll the peel up and you have yourself a beautiful tomato rose as presentation. People will be impressed!!!
....As others have said tho, chuck them in some boiling water :o)