Help me with sizing photos.....HELP!!!

Many of my photographs lose "something" if I try to crop to common sizes (8X10,16x20,etc). My print lab (WCI) prints basically any size required. I've noticed that many photo gallery sights have odd sizes. I first try to crop to a standard size. But.....is it normal to have odd sizes when selling prints? Any rules of thumb? I really do not want to compromise my work by being forced to crop to a standard size. Please Help!!!!!

None of the standard print sizes have the same aspect ratio.

4x6 = 1:1.5
5x7 = 1:1.4
8x10 = 1:1.25

So there's no way to print one file on all 3 print sizes without getting something cropped.

You need to crop to the correct aspect ratio for each print size.

You can put your uncropped image on any size print you want. For example a 20D image is a 2:3 aspect ratio and you can fit it nicely on an 8x10 print but the image only fills 6x9 of the 8x10. The result is you get a white border around your image which I find quite accepable. Dennis