For anyone shooting with Canon bodies, or using Canon EF lenses on a budget the 50mm F/1.8 is highly recommended as a lens to start out with. The plastic body won't take abuse out on the field, but for under $100 dollars it offers a fast wide aperture, sharp images, and a shallow depth of field. This is an EF (not EF-S) lens mount, so it will cover a full frame camera like the 5D / 6D or work on any other Canon DSLR. This will also work on BlackMagic Cinema Cameras with the EF Mount.
If you're just working with basic kit lenses, here's the time to grab the nifty-fifty. The Canon 50mm f/1.8 II Lens drops down from $125 to just $99 bucks when added in cart via Adorama. (click More Details on the Product page to see this price) Brand New, USA Warranty, Free Shipping, and 4% Reward *(found here).
Canon 50mm F/1.8 AutoFocus Lens