I've been quite happy with my Planet Bike SuperFlash taillights. I can attach them to my seat bag or the frame or my body. But how do I really know how good it is? I can only guess. But I have seen one from a quarter mile away in the daylight, so that's pretty good. It's visible from the sides, too, which is important.

I've heard that the Cygolight taillight beats the pants off the SuperFlash, so if I were buying a taillight, that's what I'd buy. It's not even that much more.

Don't think that a taillight is more important than a headlight. It's not. A headlight prevents collisions more. The "left hook" is a maneuver that is one of the biggest of car/bike collisions of the type where the car driver is at fault. The driver is oncoming and then turns left in front of the cyclist. The headlight can mitigate this risk. Rear end collisions are actually pretty rare.

Even though you don't plan to ride at night, you should still think hard about whether you want good lights. But of course, you don't have to decide this right away.