Are there any well known mathematicians who published very little?
Speaking of great mathematicians, I must name Harish Chandra (11 October 1923 – 16 October 1983). Well, he had more than 5 publications. but at most one or two per year. This Indian American mathematician worked on Lie groups.
References: 1, 2, 3, 4, 5
I must add Grigori Yakovlevich Perelman (13 June 1966 – ) to this answer. This Russian mathematician has made landmark contributions to Riemannian geometry and geometric topology. Mostly famous for his work on Poincaré conjecture, this man was nominated for the Fields Medal in 2006, but declined to accept the award. This list shows an incomplete list of publications so far (but remember, he crossed 40 years!) - see 900 sit-ups a day's comment.
References: 1, 2, 3, 4, 5
It seems that Evariste Galois has published 5 papers before he died at 20. See here.
For sure he is well known so he should satisfy your request.
If ancient (but not so much) mathematicians are allowed, I propose
Maria Gaetana Agnesi
http://en.wikipedia.org/wiki/Maria_Gaetana_Agnesi
as far as I can check, she published three manuscript.
Oratio qua ostenditur artium liberalium studia a femineo sexu neutiqua abhorrere, Milano, In Curia Regia, 1727
Propositiones philosophicae, Milano, In Curia Regia, 1738
Instituzioni analitiche ad uso della gioventù italiana, Milano, Nella Regia-ducal Corte,1748