First its recommended to have sbt installed. Also, I love giter8 which lets you setup your project structure layout like a snap.
Play is an awesome MVC framework inspired by Rails, so if your background is Ruby on Rails you'll love Play.
Recently, I developed an API using LiftWeb which is a lightweight full-stack web framework. It has many features that you may not find in other Scala frameworks like Comet and ajax support.
I dont have experience with developing UI with Lift, but the API I designed using Lift's net.liftweb.http._ can handle more than any application I developed using Ruby.
On the other hand, if you want a solid Database library, I used Squeryl and Slick, and for MongoDB: Rogue by Foursquare.