Intro: Reusing Lightbulbs: As Planters or Mini Terrariums
Light bulbs can be recycled in many forms and uses, although is not a new idea, check this site about reusing light bulb for chemical glassware testers , pretty cool, and here's another one using the same idea for a hanging vase and for salt and peeper containers (in french), it can be an excellent gift for Valentines (if you are in to that) or for any other day of the year. Finally back in my country in small town fairs they still use them as targets for shooting with airguns, which is better than just toss them in the trash I guess.
Hollowing the light bulb:
There are several instructables that had covered this already, although I first saw it in this site: DIY Hollow Out A Light Bulb, a very good step by step instructions in how to gutted out the bulb, (and also how to used for tester vessels for boil water and some other uses).
Here is another instructable about "How to hollow out a lightbulb and make a stand for it, pretty neat too.
and here a bunch of instructables more about light bulb uses an related stuff. Enjoy