There are a group of bees called the euglossine bees or the orchid bees that pollinate Catasetinae and Stanhopeinae tribe (Stanhopea, Coryanthes, Gongora etc) of orchids. The male bees try to collect the fragrant oily compounds that the flowers secrete, these oils are what make them attractive to female bees.
Heres a great video which shows these beautiful iridescent bee visiting a Gongora in wild. If you see this video clearly there are pollinia stuck on the back of the second bee that tries to visit the second flower
There is also a nice scientific clip which explains the pollination via some computer animation.