I will just mention more aggressive use of antiperspirants.
If that is not enough, for a lot of money, but probably less than a decent suit (unless you are me, and buy from thrift stores because ebay is too expensive), you can have a dermatologist zap your underarm sweat glands. I think this is permanent and effective, if overkill for most people. If you are ruining suits, it might be worth considering.
