I have this lights on my main bike (and probably soon i'll buy a new pair for the others).
I bought on a local chinese store but on ebay is plenty of this type (they are called "Silicone Bicycle light").

Pros:
- Lightweight;
- Nice appearance;
- You can apply where you want;
- Awsome price (1 euro);
Cons:
- Not the best light;
- Is good only for beins seen by car-drivers;
- in a road with the natural moon-light you can't see anything, just a bit the road;