It took me a while to figure out the right way to get JSF2 dependencies in Maven. The right solution is:
<repositories>
<repository>
<id>sun</id>
<url>http://download.java.net/maven/2/</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>com.sun.faces</groupId>
<artifactId>jsf-api</artifactId>
<version>2.0.3-SNAPSHOT</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>com.sun.faces</groupId>
<artifactId>jsf-impl</artifactId>
<version>2.0.3-SNAPSHOT</version>
<scope>compile</scope>
</dependency>
</dependencies>