Hi - I know how much I hate it when I start to get sweaty too. One tip, make sure you blot with a tissue and don't wipe. There are a lot of blotting papers out there too, don't really know which are best or worst. I used Bare Escentuals for quite a while and recently switched to IT Cosmetics and do like it, haven't done a major 'sweat' test yet, but hot weather's here, so we shall see. If you choose Bare Escentuals they have a product called Mineral Veil, which goes on over your foundation, it's like a finishing powder and you can use repeatedly throughout the day.
I'll be watching to see what other people recommend, I hope there are some good ideas re: sweating through your makeup or having makeup meltdown. If you don't mind will you come back and let me know what you try and if anything does or doesn't work for you. Thanks and good luck with this.