Rushton's recommendations are all excellent. I would add "Les Illuminations" to his list. It is an orchestral song cycle, solo voice and orchestra. I recently picked up a Naxos disk of Britten Orchestral Songs which include Les Illuminations, Quatre Chansons Francaises & Our Hunting Fathers for $6 on Amazon. Great performances (Felicity Lott and Phyllis Bryn-Julson & English Chamber Orchestra) and decent recording quality. Good luck! As a side note I've always thought Britten was a great entry point for "modern" classical music.
