Having tripped over tent guylines in the dark any number of times, I insist on reflective guy lines:

--Kelty Triptease
--Gossamer Gear EZC2
--Lawson Equipment Reflective Glowire

The last is by far the least expensive because it's currently on sale and (with another 5 cent purchase) has free shipping. I have not, however personally used it as I have the other two. The two I've used (and I can't see from the specs that the Lawson Glowire is any different) hold a taut line hitch extremely well.

I especially appreciated the reflective guy lines one cold early October evening (temp about 20*F, windy, and pitch dark with no moon) when I had to wander quite a bit around an oxbow-shaped stream to find a place where I could actually get to the edge of the stream to get water. I got a bit disoriented on the way back and found my tent only because the reflective guy lines clearly reflected the light from my headlamp from several hundred feet across the meadow!

Edited by OregonMouse (01/27/13 11:27 PM)
Edit Reason: correct spelling of "taut"
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey