My wife doesn't like colored stones, so emeralds and sapphires are right out. We are looking at Moissanite stones. Not synthetic, but significantly cheaper than diamonds.
We chose moissanites as the primary stones in my wife's engagement rings and everyone talks about how pretty it is. It's a bit more "firey" or "sparkly" than a regular diamond (because of more birefringence), but I guarantee no one outside a very highly trained jeweler would know the difference (if that's important to you). It's worth it to spend the money on the higher quality ones though, since just like diamonds, the inexpensive ones will have yellowish or greenish tints. Even still, they're at least an order of magnitude cheaper than similar diamonds ($600 vs. $6,500 at my quick search for ~1 carat).
Go for it.