This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
sl4j is a logging abstraction it is not a logging framework. You can use whatever logging framework you would like but you must have sl4j on the classpath. If this is a new project I would recommend using Logback over log4j but either work with sl4j.
Here is a post where a portion discusses configuring sl4j and logback.