Yesod comes with a fairly comprehensive set of libraries. Templating is handled by the Shakespearean languages, type-safe URLs are default, and Persistent is the go-to database storage layer. Many users love this combination. But there's no such thing as one-size-fits-all.
This repository contains some proof-of-concept libraries and examples for mixing and matching alternate components, particularly pulling options from Snap and Happstack. This is a testament to how well designed these libraries are (they can easily be plugged into a completely separate framework), and how simple the Haskell type system makes integration of code.