The EF 40mm f/2.8 STM pancake lens is a great and cheap lens from Canon.
Canon USA direct store currently has a great deal on this lens.
Refurbished Canon EF 40mm f/2.8 STM lens – $111.99 – at Canon USA Direct Store
This is lowest price ever for this lens. Regular price for this lens is $149.00 at Amazon.com and B&H Photo Video