a lot of people who like to film stick to primes. Especially the 85mm 1.2 and the 50mm 1.2 are well-loved because of their low-light capabilities, but they are very expensive... Usually you won't want to be zooming while filming (it looks quite amateuristic), so primes are a good choice since they give more performance for a lower price. You have to figure out what kind of price/performance ratio suits you best to figure out whích prime(s) you want though. I'd take a look at a nice wide-angle prime too, that can be quite nice if filming while driving. (I'm imagining your camera bolted to the steering wheel with a gorillapod now, nice!)
good luck on whatever you choose, I think you can get some nice stuff for 1500 bucks.
 since you're going from cairo to cape town, think about getting weither sealed lenses
@ Jaemok: could you explain how to setup a camera (I have a 5D) to automatically take a picture every 10 minutes or so? Do you need a connection with a computer to do that?