I have not seen any that can go either on the chest or the back, however I have seen "sling" type things that can go on the back or chest. Here is some info below from Amazon/Babies R Us on carriers.
I would also add -- you might want to wait until after the baby is here to shop for this item... I tried out three carriers and two slings before I found the one that was right for us. I ended up loving it and have just recently stopped using it. (20 month old still fit in it, weight-wise, but was so long it was no longer comfortable for me.) A friend - whom I borrowed one carrier and one sling from - got hers from baby showers and never liked them, never used them. Some are just so awkward to put on, some are too hot (too much padding), some not comfortable, etc.
I really don't know how people survive without a carrier, but that may have just been me and my lifestyle. But we used it so much - invaluable. I still miss it and have been debating trying to find a sling that he can still fit into.
I will look around and see if I can find some sling info for you. ~ Suzie

Here is a link that might be useful: Carrier info

I did find the one I was trying to remember - it's an Evenflo model that accommodates up to 26 pounds, I think. You can use it in the front when they're infants and then turn them around when they get older. Most of the reviews are good; but I think it depends on the preferences of the infant and also the height of the parent. So we'll see! I found it at Target so I just added it to my registry.

I also plan to save gift receipts for everything I can, and not open a lot of things until later so it can possibly be returned.

Here is a link that might be useful: Front and Back Pack

Slings that can be used on front or back ---
http://www.mayawrap.com/
http://store.yahoo.com/breakoutbras/otsbhslings.html?source=oversling
~ Suzie

You talking about carseats?

Mine was Evenflo and it worked great. It didn't get sold in my garage sale - too bad you don't live closer!!!