It depends on what you are going for.
"Normal" lenses give you an image that is similar to how the eye sees. For 35mm film cameras, that's around a 50mm lens. For Nikon and Canon digital SLRs, it's about 35mm. For medium format cameras, around 80mm.
When you start getting lower than those numbers on those specific cameras, it's a wide angle lens. It packs more field of view into the same space and gives the illusion that front-to-back distance between objects is larger than it is.
Going higher is a telephoto, which narrows your field of view so you can grab details at a distance, and they tend to give the illusion of compressing distance.
On a 35mm film camera, the 50mm would be a normal lens and the 100mm would be a telephoto.
On a digital SLR, they would both be telephotos.