Try 'Earl' it spawns you on a small island with 1 tree and a good cave system. if you go further you will find mushroom biomes and 10 block islands with lots of sand
Send The Pain On - this seed gives a world of ocean, mycelium islands with mooshrooms, a few grass islands, and a single island in the southeast corner with trees where normal mobs can also spawn sometimes. Me and my friends have a good game running, plenty of underwater caves and we recently found an abandoned mineshaft and visited the nether.