If you're looking at the fiber cables that are used with computers you're going to have a bit of difficulty. The fibers are very thin -- very difficult to stuff light through and then requires a lot of fiddling dealing with that small signal. Look for fiber optics that are used for lighting purposes, but then you're going to find that those optics are pretty expensive.
If you're just messing around I'd suggest trying pen lasers and phototransistors instead. You don't want to use photoresistors (CdS cells) because they have a very slow response time compared to a phototransistor or photodiode.