I'm having a ton of fun messing around entering random stuff. Here are a few noteworthy ones-
Harvest Moon - Very pretty. Ton of trees where I spawned, mix of dirt and sand soil. A nice lake at the foot of some cliffs nearby. Snow biome with canyonlands to the south, saw a huge natural arch and a very tall waterfall.
unladen swallow - Now, this one was interesting, will have to explore it more later. Big gaping cave near the spawn point. Good mix of soils, lots of flowers, and saw at least half a dozen small sky islands.
enirboreh - This is a pretty cool one (herobrine spelled backwards). A really tall lavafall near the spawn, and some great canyonlands. Part I walked was mostly snowy. Only issue would be the lack of trees. Screenshot - enirboreh.jpg