Originally posted by FantasticMrFox You cannot go wrong with the aforementioned DA 35 f/2.4 and DA 50 f/1.8. Great optical quality at a ridiculously low price.
If you enjoy landscapes you might want to try ultra-wide angle. Have a look at Samyang primes, like the 14 f/2.8.
I concur. Though, unless you have K-1 or want to use the lens on film cameras, I would recommend Samyang 16mm f2 instead of the 14mm. Not as awkwardly wide, a little easier to focus, slightly faster aperture, removable lens hood.
You can also look for a DA 40mm XS. Affordable and super compact, with the "limited style" deep contrasts, but it has slightly slower aperture. Still, the K-r with DA 40mm XS is a really small package with good quality photos and fast AF.
Tl;dr: You can't go wrong with DA 35mm, DA 40mm XS, DA 50mm f1.8, Samyang 14mm, Samyang 16mm. All of these are really good and affordable, great place to start with primes. Personally, I would go with DA 35mm as an everyday lens or Samyang 16mm for significantly wide angle. My first prime after buying K-r was DA 35mm and I don't regret it. Still use it a lot today, years later