Binoculars

Birding
Astronomy
Close-up
Add-ons

Ontario Field Naturalist's Toolchest
Birding
The requirements for birding are met with most binoculars in the field.  If you are casual about birding, cheap binoculars will suffice.  Mid-range binoculars with give you better optics and many mid-range binoculars are often good for astronomy and/or looking at bugs. The high-end binoculars give you top notch optically quality, but at quite a high price.  And if you forget to clean your high-end optics you are sacrificing much of the advantage these binoculars give you.  A good choice are 8 * 42.
 
Astronomy
If you use your binoculars for astronomy you will get better performance if you choose a larger aperture.  7 * 50 are popular, as these provide a good mix of light weight with light gathering power.  You can go for higher apertures but you will need a mount to make the most of them.  Another feature is the ability to focus past infinity.  In low light levels you eyes might not focus at infinity, and the ability to focus past infinity will compensate for nighttime myopia.

Close-up
Looking for butterflies or dragonflies has become popular rather recently so the choice of optics that focus closely are limited.  A close-up pair should focus to about seven feet at minimum.  Five feet is better and many can focus as close as three feet.  One pair of binoculars can get within 1.6 feet and a rather specialized setup can get closer.

Add-ons
On the Bushnell Elite model of binocular you can purchase an add-on that will increase the magnification 2.5 times.  This is good as a low grade spotting scope for occasions when carrying a spotting scope is not practical.