Judy -
I would recommend a very good book on suiseki. It's called The Japanese Art of Stone Appreciation, by Vincent T. Covello and Yūji Yoshimura. It goes through the classic Japanese stone classifications, and gives a very good description of what to look for in stones.
I have found many nice stones in the past. Some I would call suiseki (fitting in to the Japanese parameters), and others I simply consider viewing stones. I tend to call Japanese style stones suiseki, and try to define others as they fit. Kind of like differentiating between bonsai and penjing. For example, in suiseki you likely won't find a stone that has been altered through polishing, etc. However, in the Chinese art of gongs
Anyway, the book above is really good and it's not too expensive.
Good luck!