The standard pieces would be the works of Sor, Bach (original lute works & transcriptions), Albeniz, Carcassi, Carulli, Coste, Tarrega, Giuliani, Newsiedler, etc. Here's an interesting source for downloadable guitar sheet music: http://eythorsson.com/music/
It took me all year to learn recuerdos de alhambra. I can play it now from the start to the end but have many fumbles in between. Think I need formal training leow..
This piece is very good for learning right hand plucking control.