Blue Eggs
The "classic" blue egg layer is the Ameraucana, but getting consistently blue eggs from sexable chicks has always been a problem.
Male chicks have a white spot on the top of their head.
Distinctive crests
Cream Legbars
The crest is not important for egg production, but you have to admit - it is cute!
Also known as Crested Cream Legbars and sometimes abbreviated as CCL, these are still fairly new to the US and not commonly available. The reasons for their popularity are:
1. Lay lots of large, blue eggs
2. Autosexing - you know the sex of the chick at a glance
3. Crest makes them stand out in a crowd of hens
4. Small and alert like a leghorn, but much calmer around people