We all know imagecache is a great module to grab images of any size that are in your site's files/ directory, but sometimes it's hard to get every image to be the right size without black borders on the sides or top. The trick is to know the proper "order of operations".

Here's a fast recipe for square thumbnails that will work with landscape or portrait picture orientations:
Scale - width: 85, height: , upscale: No
Crop - width: 85, height: 85, xoffset: , yoffset: top
Scale And Crop - width: 25, height: 25

This is a recipe I use for user profile pictures, and it handles very wide or tall images well. Adjust the values proportionately to fit your needs. Step 3 is an optional step I apply in order to make a super-small thumbnail in certain places in the theme.

NOTE: the original size of the picture in this case is usually larger than 170px, but at the very least, it should be larger than the size of the initial scale. If you are starting with a very small picture, this recipe won't work as well.