Ailsean, Spekkosaurus, and the "Team Gato" Team are three of the most owning owners that ever owned the Chrono series OCR scene. I just can't get enough of that Frog-meets-Steiner-meets-Ants Go Marching combo, Spekkio revealing his Scottish side, or Gato's "terrible" karaoke...
DJP's kickin' banjo fair mix, several of the Schala mixes, and JAXX's mixes also stand above the rest, but admittedly, most of the knock my socks off (CC mixes included).
I didn't particularly like CotMM's work with the Magus theme, but that style is also not something I favor in general. I did like what he did with the Ocean Palace theme, though.
Outside of the Chrono mixes, I don't have very broad horizons for what I've listened to or downloaded from OCR - yet. I've gone through the entire collection of mixes from the Metroid series, and I have to say, there are quite a few good ones there. Ailsean continues his trend of kickin' arse, Vigilante takes "atmosphere" to a whole new level by basically creating the feeling of being on Zebes with "Zebesian Midnight," and both AmIEvil and The Wingless contribute several excellent mixes to this group.
Outside of that, I've only listened to a few particular songs suggested by friends: Ailsean's "Terra In Black," The Wingless's "Godspeed," and Rayza's "Frozen Knuckles." Although, I have to admit, the vocals at the beginning of Rayza's Sonic mix, there, are a bit disturbing... Jamaican Sonic... ugh.