Relevant article on the synthetic diamond trade from Wired last year: http://www.wired.com/wired/archive/11.09/diamond.html
edit: oops I mean 2003; 11.09 was the issue number
edit: oops I mean 2003; 11.09 was the issue number
A good alternative is Canadian diamonds, which are not owned by DeBeers, not mined or polished by slaves, and not the cause of any conflict. That solves about half the problems with diamonds.
Get them from Brilliant Earth (I'm not employed there, just a very satisfied customer.)
Not that that makes it immoral to do so. I wouldn't go that far.
That said, a one karat stone is no good as a solitaire (the book from the article above talks about this: one karat stones all go into eternity rings, which were invented by debeers due to a massive oversupply of Russian one karat stones. Actually, the book implies that these stones may have been lab stones, as no-one knew where the Russians got so many one karat stones from.)
http://en.wikipedia.org/wiki/Moissanite
Someone would have to really study the ring to realize it wasn't diamond.
Plus it first came from meteorites which puts it high on the geek scale ;)