Depends on spindle speed.
If you are using a trim router or other high speed spindle then I'd start with plain router bits for wood.
If your spindle is slower <10000 rpm, and you are cutting aluminum, I'd start with 2 flute HSS endmills (try Shars tool co.), then graduate to 3 flute polished carbide endmills (ebay: YG alu-power)
Plan on crashing, plan on breaking endmills, plan on clogging flutes, plan on ruining your work. Learn while you do this and you will quickly get the hang of it.