Well, all the recorders mentioned in this thread have internal mics [edit, not true, 60D apparently doesn't, see following posts]
The DR2d rocks, but I don't consider it a great 4-channel recorder at all, rather, to my way of thinking it is a 2-channel recorder with the welcome but very limited capability of recording 4-channels as two stereo pairs, is capable of fitting into a pocket, capable of running 5 hrs on internal batteries, satisfies my sound quality requirements, and is inexpensive. Since no other recorder has that same feature set, it automatically wins the "4-channels in a pocket" category by default. Other than that it's actually pretty terrible as a 4 channel recorder. But it works and there are no other contenders for it to compete with.
IMO the R-44 is a great 4 channel recorder. And although I've only handled them a few times and do not own either, both the DR60 and DR70 seem far more capable, adjustable and easier to use as four-channel recorders than the DR2d.
[edit]- Here's an analogy: I use a DR-680 and am very happy with it. In my opinion, the DR-680 is not a very good 8-channel recorder. It is a very good 6 channel recorder which has the capability of recording a total of 8-channels of input, awkwardly. Similarly the DR2d is a good 2-channel recorder which can be pressed into service to record 4-channels, awkwardly. They can do those things, but they can't do them "great".