Playroom Music

Something that I have been thinking a lot about lately is music for the playroom setting, since I have been starting to use the playroom a bit more. I decided it would be nice to share my thoughts with others on the topic, and perhaps lay down a basic set of guidelines for what makes music 'suitable' for this setting.

A few things I've considered:
1) The music should have little to no vocals (preferably none), this is distracting.
2) It should carry a fairly steady beat, ranging from moderately fast to moderately slow, with not too many abrupt tempo changes.
3) Volume is key, so the volume should not change rapidly or with too much variation
4) Avoid noises that in another setting might eventually become an annoyance (sirens, squeals, very low rumbles, etc)
5) It is best if the music runs together a bit from song-to-song, to more easily lose track of time.

The music that ive found that seems to fit this best, is Techno/Dance/Electronica/Trance, for obvious reasons. I have a few selections that i like in the playroom right now, but am looking to expand.

I'll pose this question here, respond in comments and perhaps we can get a bit of a dialogue going: What music do you suggest for the playroom (either artist/album or genre). Additionally what traits do you find defines good play setting music?