If you do decide to donate miles, consider http://lbeh.org/

They take donations of cash and miles to fly active duty troops home to see their loved ones during the holidays. The folks doing the work are volunteers so all the money actually goes to the troops.

Better still it's even tax deductible. If you donate miles, they make an estimate of what that ticket would cost using cash and send you a receipt for your tax return.

I've supported them since their inception in 2001.