Jay-Z & Beyonce Gussy Up for Rihanna's Charity Ball

Jay-Z and Beyonce clean up good ... lookin' even better when it's for charity.

The couple hit up Rihanna's third annual Diamond Ball in NYC benefiting RiRi's foundation that pours $$$ into impoverished communities around the globe.

Bey got a little help from Spanx but, seriously, who the hell cares? She looks super hot and very superhero-ish. RiRi's party was packed with celebs -- Kendrick Lamar performed and Dave Chappelle also grabbed the mic.

It didn't end there -- Calvin Harris, Future, Lil Kim, La La Anthony, Fabulous and Young Thug also hit up the shindig ... and all for a great cause.