a good all arround lens is the 18-200mm f3.5, you can take this on vacation & is usable 80% of the time, a nice 50mm prime lens is also a good idea & ofcourse a Micro lens maybe a 105mm, these are not cheap pieces of glass so go to a nice shop & shoot tith it first, also remeber that you will want to get a tripod once you get into macro shooting
That is good advice for someone who is passionately interested in photography.
however
it is a large monetary investment for someone who really wants something fun and easy. I travel with four different lenses for different occasions because I want to be able to get the best possible shot I can get. But I purchased those lenses one and a time as my interest and love of photography progressed. For someone who might only ever have an occasional, hobby interest in taking photographs ( the kiddies, pets, vacations) I think that kind of monetary investment is a little extreme (unless you have a lot of disposable income. In which case, go right ahead).
Most digital SLRs do come as kits with a lens. That might be the easiest and cheapest way for you to go. If you are going with someone with a kit lens, a 28-80mm will do the job, or an 18-55mm. Those aren't fancy but are perfectly serviceable for a beginner.
I am assuming your wife is a beginner, or she would have requested a specific lens.
If you want to go with something fancier, a 17-200mm is nice. I shoot most often with the 17-250mm tamron lens, but that will set you back about $500. I also have (in order purchased) a 17-35mm wide angle (I think I paid $300 for this), a 100mm macro ($600, I think), lensbaby swing lens ($150).
Whatever lens you decide to get, make sure you get a UV filter for it to protect it from scratches. This is extremely important.
