I get my blasting media from Key Abrasives, I recommend new and experienced people check out their website as it hosts a wealth of information about all the different types of media they sell and its uses.

I use a medium Iron Silicate for heavy work Cast Iron, rusty steel plate etc. and have 3 different grades of glass bead down to 75 microns for polishing aluminium. Its so silky smooth its like nothing I've ever had my hands on, its cool to the touch, softer than silk and feels thinner that water (not to be confused with crushed or recycled glass).

Once I've got my printer running a bit better and gained some experience I'll no doubt be throwing a few items in the cabinet to see what's what.