What's required to have sbt build with Akka?

You didn't have all right dependencies for your project.

You have add this one "com.typesafe.akka" %% "akka-actor" % "2.0.5". This one is the main dependency with the core modules for akka. Also it's better to add the following ones for your akka project:

"com.typesafe.akka" %% "akka-actor"    % "2.0.5",
"com.typesafe.akka" %% "akka-slf4j"    % "2.0.5",
"com.typesafe.akka" %% "akka-remote"   % "2.0.5",
"com.typesafe.akka" %% "akka-agent"    % "2.0.5", 
"com.typesafe.akka" %% "akka-testkit"  % "2.0.5"% "test"

And to use actors you should import akka.actor._

Updated

Ok, this build file works for me

name := "hello"

version := "1.0"

scalaVersion := "2.10.1"

libraryDependencies ++= Seq(
  "com.typesafe.akka" %% "akka-actor"   % "2.2-M3",
  "com.typesafe.akka" %% "akka-slf4j"   % "2.2-M3",
  "com.typesafe.akka" %% "akka-remote"  % "2.2-M3",
  "com.typesafe.akka" %% "akka-agent"   % "2.2-M3",
  "com.typesafe.akka" %% "akka-testkit" % "2.2-M3" % "test"
)

Don't forget to reload and update your project in sbt