There are three mass-market paperback editions. The first has
this cover and dates from 1999. The second has
this cover and was published last year. The third has exactly the same cover but is half the price and has a new introduction by Steven Erikson and came out yesterday.
I suspect there will be tremendous confusion between the second and third editions. The difference is the new Erikson introduction. If you have it, it's the third edition, if you don't, it's the second.