I used to be able to buy music mp3s from United using miles but unfortunately, they no longer sell them. :(
If the miles get close to expiration, I will donate them.
ETA: Thanks for starting this thread!
I just checked United.com and I can use miles to get a reimbursement of the $95 annual fee on my Chase/United Visa! It's only good within 3 months of paying the fee and it will cost 11,875 miles. I have about 12,000 miles and will get another 50,000 after this month's spending gets paid. Going to do some math & consult DH to see if I want to do this.