Altec-Lansing 641's if music is important to you. Logitech Z-560's if music is not important AND price is your most important factor.
I just went through a major shopping expedition for speakers in this price range. Got it narrowed down to the 641's and the 560's. I ended up with the 641's, and they are incredible. A couple factors made me spend the extra $35 that the 641's cost - here's a rundown on what I found and my personal opinions (pros and cons are specifically comparing 641's vs. 560's, not other speakers or on an absolute scale)-
Z-560 Pros:
1 - less expensive (135 vs. 170 approximately)
2 - small, attractive satellites
3 - smaller bass unit box size
Z-560 Cons:
1 - sloppy bass (lots of it, but not very well defined)
2 - nonexistant midrange (poor blend between bass unit and satellites)
3 - really flimsy remote unit (knobs feel like they are mounted in Jello and ready to fall off, also unit tips over really easy and looks cheap, plus no markings on knobs and no treble control)
4 - bass unit looks like a toy
5 - questionable build quality (looked at 5 stores, the 560's were broken or failing at 5 of the 6 stores - doesn't really inspire confidence)
641 Pros:
1 - tighter, deeper, more accurate bass
2 - good midrange response and far, far, better blend with woofer
3 - more accurate-sounding highs (less artificial "sizzle")
4 - excellent, heavy remote with optical control knob (doesn't fall over, come apart, and no chance of noise, ever.)
5 - outstanding build quality (parts and controls just have a very high quality "feel", construction looks like it will last forever, looks very expensive)
(edit) 6 - forgot to add - sounds better at low volumes!
641 Cons:
1 - costs a little more
2 - satellites are sort of big (about 2x the Logitech's)
3 - bass unit is gigantic (about as big as a mini-tower PC)
4 - I don't really care for the very dark blue color of the enclosures, but it's pretty close to black...
BTW, I have listened to the Swan's M200 and the Altecs make them cry. No comparison whatsoever - the Swan's sound good but the Altec's sound better. The M200's weigh just under 30 pounds for the pair - the bass unit alone for the Altecs weighs more than that, the whole system weighs 56 pounds, as if that really means anything!
The short story is that the sound and the looks of the Altec 641's would be suitable for a "grown-up's" living room, the Z-560's would be more at home in a dorm room. Both can blow your eardrums out, but the 641's sound better for music and seem like they can take a pounding much better than the Logitech's.