Well, what's your budget?

Taillights --

http://www.dealextreme.com/details.dx/sku.35036 $3.54 taillight, good quality, great price. Really, at this price, as good as this light is, I'm hard pressed to suggest anything else unless you've got lots of money to spend.

Most of dealextreme's older bike lights are crap, but some of the ones they've added recently are good, and the ones I suggest are in the latter category.

As for headlights ...

http://www.dealextreme.com/details.dx/sku.18307 $7.43 good quality, great price. Ideally, get rechargeable AAA batteries to go with it.

If you've got $55 to spend --

http://www.dealextreme.com/details.dx/sku.16501 $36.21 light
http://www.dealextreme.com/details.dx/sku.8274 $1.54 mount
http://www.dealextreme.com/details.dx/sku.5790 $8.18 two batteries
http://www.dealextreme.com/details.dx/sku.1251 $12.30 charger

If you've got $95 to spend, get the Magicshine 900 from Geomangear.

And if you've got some more money to spend and want to "bling" up your bike a bit and help it be seen from the side, get the Disco Spokelit for about $7. Around here, Academy carries them.