Another vote on dowels!!! I bought mine at the craft store. In the wood projects section. They are really long....but, just saw them in half and voila! Perfect guide.
I put wax paper down, a hunk of dough,dowels on either side of my dough, then another piece of wax paper..... I roll over the wax paper...helps to not stick. AND, to not add any extra flour to your dough.
I ice on the bottoms of my cookies - completely flat surface. Also...I think several CC'ers have mentioned the "double cut". This is especially helpful for me....because I use a traditional sugar cookie recipe. It raises and puffs up/out pretty good. So, when the tray comes out of the oven, I do a quick re-cut with the cutter I used & I have a nice crisp & clean cookie. Makes a big difference!