The Samyang/Rokinon lenses are about the cheapest cine-style lenses in existence (and most of them cover full-frame 35mm), which means both the iris and the focus rings have gears for a follow focus, and the iris is measured in T-stops, and is smooth so you can ramp exposure during a shot if necessary. For example, if you're starting a shot inside and need to go outside, or if a cloud goes behind the sun right in the middle of shooting, you can change exposure. There are many reasons you'd want cine lenses, but until these lenses they were just not affordable in any way -- and now they're even cheaper.
B&H is running a deal where you can get these three Rokinon cine lenses in Nikon F, Canon EF, Sony Alpha, or Sony E-mount for just $1,300 (these are basically the same as the Samyang except they are branded differently):
If you bought them separately they would be a little less than $1,600, so you'd be saving about $300. The cine lens range also extends to an 8mm T3.8, 14mm T3.1, and 16mm T2.2. These may not be the perfect focal lengths depending on your format (they are still missing a 50mm lens which is apparently coming), but you can also add a few lenses to fill out the whole line. For example, adding the 16mm T2.2 lens which is designed for APS-C/Super 35mm cameras gives you a real wide option on that format, and you could add a 50mm lens from somewhere else to have a relatively complete lens set.
Matthew Duclos has said some interesting things about these brand of lenses, and Luke Neumann did a test of probably the weakest lens in the bunch wide open, the 24mm, to see how it compared to other cinema lenses:
Video is no longer available: www.youtube.com/watch?v=73rxg-yxTr4
These lenses are also useful if you're adapting them to other cameras that can only take a manual iris lens. For example, if you bought the Canon EF mount version for a Canon DSLR, and wanted to use them on a Blackmagic Pocket Cinema Camera, you could use them with just a cheap dumb mount, and not have to deal with the mounts that try to give you a fake iris to stop down.
The sale is only until December 3rd according to B&H, but occasionally these are extended. Check out the lenses from the links below.