I find the Sigma 150mm macro lense is, for me, an ideal focal length for taking close-up shots. This is especially true when it's insects and other creatures which may be scared off if you poke a camera too closely at them.

This is a fast lens, with a maximum aperture of f/2.8. This, for me, is not always absolutely neccesary as I tend to use a tripod to allow slower shutter speeds and a smaller aperture to give me the depth of field I need.

The build quality of this lense is excellent and I like the satin finish though I have heard other photographers complain about this.