Ever since I first saw Some Like it Hot (which was when I was 10ish years old), and Marilyn Monroe (as Sugar Kane) asked, "Are my seams straight?" I have wanted backseamed tights.
They are super classy, remind me of the 1940s, and are just so cool and sophisticated looking. Now, if only I had some place to wear them...
Upon Google searching, I found quite a few different (albeit pricy) options:
Casablanca Backseam Tights, from ModCloth
Gerbe Backseam Fatal Tights, from Mytights.com
Hue Backseam Sheers, from Lori's Shoes
Sheer Luxe Back Seam Pantyhose - American Apparel