Monk Hybrids
If you are looking at ability scores, there is some match-up that can be done. Monks do seem to lose a lot by the default hybrid rules, though. You might consider a free house-ruled hybrid talent or two from the monk list if you want to preserve their flavor. I do consider it very difficult to build and play a hybrid that doesn't keep the main attack stats for the two classes pretty close to maximized, so that colors my preferences.
The dexterity primary of the monk is only shared by other strikers (and the essential hunter ranger, for which no hybrid option exists), so that is going to limit you, in my mind, to keeping the dexterity up for the monk and using the secondary stat of the monk's tradition to match with the primary stat of the other class. It's a bonus if the secondary stat of the other class is dexterity.
Defender: I think there is a fighter option that favors strength and dexterity, making it a great match for the stone fist monk. Other strength defenders would work pretty well here, too, but with loss of off-stat benefits. The constitution-using battlemind would also be a good match for an iron soul monk, but the off-stat of the battlemind would suffer, and I think you'd be house-ruling the iron soul hybrid option.
Controller: Centered breath monks align perfectly with bow-using seekers and predator druids (though use of the predator options requires hybrid talent). For a one-stat match-up, you could use the centered breath monk paired with an invoker or throwing-style seeker, but your off-stat on the other class would suffer.
Leader: There are a couple that use wisdom (cleric, sentinel druid, shaman) or strength (warlord), but none to my knowledge that use dexterity in any fashion, so some off-stat for the leader would suffer.
I hope that's at least somewhat useful, given my perspective on ability-score limits for "playable" hybrids.
