I've seen many cakes on here with the diamond design on the side of the cake -- how do they do it?? is it a tool or what?? I would really like to try it out!!!!

There are several on line places you can order one. It is a sq of plastic w/the pattern on it so all one needs to do is press it up against crusted buttercream icing to emboss the lines.
Earlene Moore sells them; I bet Global Sugar probably also does. Usually they only cost like $5.

Can you maybe post an example? Its hard to know what your talking about when we cant see an example. It could be fondant cut outs. it could be something done in buttercream or with some tool or pattern. If you can find an example Im sure someone can tell you how to get that effect.

http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1336228


this is the one that really caught my eye and made me want to try it!

found it!!!!!!! Thanks ladies!

that picture looks like the diamond impression mat.. sugarshack , shows this in one of her dvds. and sells it on her site... love it.. then there is the diamond cutter/impression tool.. jennifer dontz , shows this on her dvd... and sells it on her site.. love it also.. you can get 2 different looks.. other cake sites like..globalsugarart.com.... countrykitchensa.com.. the one we can,t talk about and other cake decorating sites will have these.. hth