Hi Scott,
What style/instrumentation of MIDI loops are you looking for? RnB, DnB, Pop, Drums, orchestral, etc?
Did you know that the Green apple loops that are bundles with Logic contain MIDI regions? You can use these with any software instrument of your choice...
Logic's Instruments and effects are impressive. Sometimes they take a bit of tweaking and layering, but you can produce sounds for almost every style of music. Reason, however, is well known to have some of the most excellent sounding synths. A lot of producers use both Reason and Logic together (Rewire technology) so they can make use of reason's instruments.
Have you checked out the Reason tutorials here to get a sense of what the instruments are capable of?
Thanks
Rounik
p.s. here are a couple of places that serve up MIDI files:
http://www.mididb.com/
http://www.dancemidisamples.com/