I have a few rules when it comes to buying black tights.
1) They must be 100% opaque and flat black. None of this sheer gloss business.
2) They can't make me itchy. Scratching in public is embarrassing, but scratching anywhere tights-related?
3) They can't do that supremely awkward thing where the control top ends up between your knees, leaving you -- the wearer -- to helplessly perform lunges while pulling up at the waistband to make sure they don't become MC Hammer tights.
Calvin Klein Ultra Opaque Hosiery in 120 Denier, I will never be without you. Not only do they completely satisfy the above three conditions, the tops are ultra-controlling and create a completely smooth, svelte silhouette under all clothes.
Layer under pants in the winter for an extra layer of warmth or under your favourite summer outfit to make it fall-appropriate. These typically run $20/pair at full retail, so I always stock up on 2-packs at the Calvin Klein outlets.
Edit: These legs belong to Tod. She has much better core strength than I do.