[driverdan]

I bought a roll of cheap 5% window tint and put it over all device LEDs. It makes it dim enough to not impact sleep but still visible.

If you don't want to see the LED you can cover it with electrical tape.

[adrianmonk]

My preferred alternative to electrical tape is a piece of aluminum foil stuck on with painter's masking tape. Aluminum foil (or any metal) is really excellent at blocking all the light, and painter's tape doesn't leave residue.

[beatgammit]

If you're not worried about residue, you can get aluminum foil tape, which is quite handy for other household repairs as well.

[edoceo]

Gaff tape.

[toomuchtodo]

Gaffers tape is the holy grail IMHO. So many good uses for it.

[sjwright]

I used to run a Dell UltraSharp 3008WFP. A great monitor for the time, but the power LED was so damn bright that black electrical tape didn't fully extinguish it.