I would also recommend APT for cutters, as well as Wealdon Tool Company. Neither are particularly cheap (there are some budget cutters on APT), but I have yet to receive a sub-standard cutter, unlike some cheap ebay sellers.

For aluminium I would recommend single flute carbide and if you use trochoidal or adaptive clearing, then get some 6mm 3 flute serrated roughing end mills for hogging out "large" volumes.

I also use single flute cutters for wood (guitars), but obviously keep a separate set for this purpose.