Hi, kittenzl,
I've got a few suggestions for bar soap embeds that may help you out. Yes, you could pour a slab of soap and use cookie cutters. I like to use a silicone pan for pouring. You may want to look online or in your craft stores for fondant cut-outs (they're in the cake decorating area). I've found heart fondant cut-out sets at Michael's and AC Moore, and the cool thing about it is that you get three sizes of hearts (small, medium, and large) in one pack. You can also get stars, circles, ovals, squares, flowers, leaves, etc. (There's lots of inspiration in the cake decorating/baking aisle!)
Candy molds seem to work well, too. I've had success with them. Be careful not to pour your soap too hot or else the candy mold can warp or melt.
You can buy embedding molds, too, from soapmaking suppliers. Bramble Berry sells some.
I haven't experimented with column molds myself, although I'd like to someday. I'd think the column molds would suit a loaf soap well. I haven't tried using metal molds, either. I would wonder if the soap is difficult to remove from a metal mold, and if the soap could possibly react chemically with the metal? Maybe someone with experience with this could better advise.
Hope this helps. It's funny how after a while, you start looking at everything and wondering, "Could I use this as a mold?"
Have fun exploring!