The Tech21 character series pedals seem pretty good. I got a Blonde and a Liverpool last week. I haven't had as much time to play with them as I would like, but they ought to sit nicely in the effects loop of an M13. (That pairing was Bill's suggestion a while back.)
The M13 seems like the natural evolution of the Line6 stompbox modelers. It makes it easy to play with combinations of effects just as the individual modelers did and more or less recreates the pedal board effect. The effects are interesting but not deeply interesting. The Vortex has more interesting effects, but it's a pain to program, a pain to switch effects on (relatively speaking), and frequently noisy. For example, Line6's tremolos are nice but they aren't the Shimmer effect from the Vortex. Having tempo sync for the effects is nice, but I don't think the M13 will sync to MIDI clock (feh, since the device does have MIDI). The looper improves on the DL4 but I think it's mono and there isn't the option of having it generate tempo information for the effects.
What would be really cool (not going to happen) would be for Line6 to take essentially this same form factor and build a multi-looper with it possibly with a couple of post-loop effects available as well. An M13, a "Loop 13", and a couple of Tech21 pedals could make for a powerful and portable rig.
Mark
