Both lenses suggested by VirtualRain are good. They're the cheapest lenses you can get. The 18-55mm is the stock kit lens with most canon DSLR so it's easy to find used at a low price as lots of people have them and are upgrading from them. For it's price, it's a good lens, it's quite versatile but it's quite restrictive because of the aperture is so small. Shallow depth of field effects are nearly impossible and forces you to have a lot of available light. The 50mm is a much better lens but at 50mm it's more of a portrait lens and not that useful for video.
If I were you, I'd go with a t2i or a t3i rather than the 7d. You can get a t2i for less than half the price of a 7d and get a 18-55mm in the deal. The t2i, t3i and 7d share the same sensor so there is basically no difference in image quality. The 7d has a much better build and ergonomics but that is more of a concern for photo. With the spare money, you could get some sweet prime lenses. You could shoot pretty much everything with a 28mm f/1.8. Get the 50mm because it's such a good deal and use the 18-55 @ 18mm when you need to go wide. Primes lenses are preferred for video as they are usually sharper and have a larger aperture at a cheaper price. You need a lot of light to shoot video and you will quite often want to get a shallow depth of field. Best of all, lenses loose their value much slower than camera bodies. Also, do you have a tripod?
Oh and the only lenses I own are the 18-55 and 50mm. I'm looking for a 28mm eventually.
