Within Muntinlupa? Depends on what specific type of venue you prefer and your budget. Fernbrook Gardens (Daang Reyna) seems to be a top choice. Other options are hotels within Filinvest City such as Vivere (Bridgeway Avenue), Bellevue Hotel Manila (North Bridgeway) and the new Acacia Hotel Manila (Commerce Avenue).
Some other alternatives that come to mind include The Palms (Laguna Heights Drive, Filinvest), Portofino Heights clubhouse (Daang Hari), Hampton Court (within Hillsboro, I believe) and Ayala Alabang Clubhouse, although all these will require member/resident sponsorship.
There's also the new big multipurpose venue, the Filinvest Tent (Commerce cor Spectrum Midway).