Only what you need for your baby. Really. (OK – and some fantastic things you don’t that are pretty cool.)
See also A Word on Toys
Also in the staring category are mirrors. Astrid didn’t notice herself in a mirror until she was 3 1/2 months old despite all expert assertions that infants love mirrors, but perhaps she was an outlier. You can tie a baby-safe one to the side of your crib to keep the baby entertained when s/he wakes up or, if you get one that stands on its own, s/he can have a nice long stare on on the floor while trying to work out how to get to it. (And when I say “entertained” I mean for, like, five minutes, not twenty. I thought I might get a leisurely shower out of the mirror thing, but no. So sad!)
Given how often I heard them recommended, there aren’t a lot of infant mirrors out there to choose from. Most of the ones I found had irritating borders and/or the “mirror” was small and made of super cheap material so it was hard to see any reflection in it at all. Fortunately, I finally found the awkwardly-named Wimmer-Ferguson Double-Feature Mirror. It has a big working mirror, ties flat to your crib’s side AND you can flip it around: the back has six black and white pictures your baby can look at if s/he’s not into the mirror itself yet. Sweet.
If you want stand-alone, I’m afraid you’re stuck with the bad patterns/bad reflection category.