The kit lenses for most dSLRs are 18–55mm with an aperture range of maybe f3.5–22, which is great for all-around photography (hence it being the standard!). If you want something with as much flexibility as you describe, I’d go for something in that range (with image stabilization if you can afford it). Then you can always get a really zoomy lens later, or a macro, or a wide-angle, depending on what you really enjoy shooting. I have a kit lens and a 50mm fixed lens that goes to f1.4 that I use for portraiture. The kit lens is good enough for everything else, and then the only thing I felt I needed was a wider lens, so that’s what I got to augment it. (And I actually use my 50mm a lot less than I thought I would!)