Having been looking for an armband for my 2nd gen Ipod Touch for some time, I decided to go with the Navitech. Although there were other cheaper options, many had reviews complaining of poor build quality and a bad fit for different sized arms.
The Navitech armband is well made and can hold all versions of iDevices it says it can. I was concerned I would not find an armband with the correct earphone jack access in the armband (as depending on the generation you have apple keeps moving the jack about), but the Navitech provides access for which ever model you happen to have.
The design is minimalist and and comfortable, with no rubbing or chaffing when jogging. I have not been able to test how water resistant it is, due to glorious weather at the moment :) but will update my review when I run in the rain. However, from inspecting the armband I am confident that it would keep my ipod dry in light rain - I wouldn't rely on it in a thunderstorm, but if you go for runs in that kind of weather there's something wrong with you anyway :P
The strap has three patches of Velcro that allow it to be adjusted for a wide range of arms whether you have large or small biceps.
The clear plastic cover allows me to access my ipod Touch easily. It doesn't cling smoothly to the surface of the ipod and I have to sometimes repeat an action, but it is what I expected and very easy to use.
The reflective patches on both sides of the ipod compartment are a nice touch, but I would not rely only on them if you are running at night, but along with a reflective vest will certainly add to your shiny look when picked up in headlights!