I think JPA is nice and convenient ( not to mention standardising, as we used to have every individual programmer doing his/her own thing with a jdbc connection).
I
Entity Framework is what you should check out first. It is recommended by Microsoft.
Other popular options include NHibernate or DBLinq.
http://community.jboss.org/wiki/NHibernateforNET
http://www.nhforge.org (later versions)
http://code.google.com/p/dblinq2007/