A few years ago I ordered a collection of colored reflective tape from Identi-Tape. It's held up well (most of the pretty colors are not DOT), it's extremely visible at night, and because of the colors, if you take some time for artful placement, it doesn't make your stuff look super geeky in the daytime.

They also carry sew-on reflective tape for your packs and garments, but I haven't tried that. Some of the flexible fabric stuff is definitely better than others. I've been really disappointed in how the reflective material has rubbed off my Amphipod harness - be sure you get something that's got a clear plastic coating over the reflective stuff.