The Blinky 7 more than covers the basics. Five LEDs all pointed in different directions give you 220 degrees of visibility.
And, in spite of it's name, it doesn't have to blink if you prefer a steady light, say, when you are riding with a group and don't want to irritate the person directly behind you.
Busch & Müller 4DToplight Permanent Bike Tail Light
Planet Bike Tail Light Bracket
CygoLite Metro 300 USB Rechargeable Headlight