These liners are a bit pricey but work really well to darken a room.  Many room darkening curtains are boring or industrial looking. These allow you to buy the pretty curtains you want and to also have the insulation and room darkening benefits. I have them behind slightly less wide grommet panels. They hang fine and you don't see the liners at all. I had only 6 grommets but it works to have two of the liner hoops behind one set of grommets. 

Pros: Easy to hang, block light well, quality and flexibility
Cons: kind of pricey