West Systems Epoxy is my preferred product for glassing, and doing fillet work. West Systems is the primary brand used in boat building and is available in most if not all Boating Supply shops (as well as many places online) I buy mine online at [link=http://www.newportnautical.com/westsystemepoxy.htm]Newport Nautical[/link], their shipping is only $3.95 no matter how much you purchase.

When you are using micro balloons, you want to mix it up to the consitancy of thick peanut butter. This not only keeps the epoxy from running, but it also makes the final product light and easier to sand. When you apply the mixture, tape off surrounding areas to keep excess epoxy from area that it's not needed so that it wont need to be sanded away later. Smooth it out best you can, but as it starts setting, the exothermic reaction will cause it to soften slightly and smooth out even more. For doing fillets, I like to use a syringe to make application easier and neater.