The rice genome was sequenced because of it's major importance in the world food industry and it's relatively small genome size. Since the first sequenced plant genome (Arabidopsis thalia) was a dicotylous plant it made sense to sequence a monocot next to have a broad taxonomix sampling. Unlike many of the recently sequenced genomes the sequencing has been done using a BAC-by-BAC approach a very costly a labour intensive procedure. But this yields a very high quality genome that can be assembled into chromosomes.

Publication:
The map-based sequence of the rice genome.Nature 436, 793-800(2005).