We've been using SubSonic lately, which I first bookmarked from Scott's post.
Essentially, the project is an implementation of the ActiveRecords pattern from Ruby on Rails in .NET. Or as the authors describe it, , "a toolset that helps a website build itself". I'm using it on a project I'm working on now and so far it's been very useful - though we haven't had to scale yet. We had to slightly adjust our data model to be more SubSonic-friendly, but it's pretty flexibile and even supports stored procedures if you're into that sort of thing (we are). It also "singularizes" the database tables - i.e., a Companies table becomes a Company object, and a Books table becomes a Book object. (Though it does strip the last 's' from Business.... I'm reminded of that old 1-800-MATT-RES commercial).
Regardless of future experiences, I can wholeheartedly recommend it to build a DAL for prototyping.