Apparently throughout the weekend and/or until stock runs out you can buy the OnePlus One without an invite, as long as you get your orders in you're guaranteed delivery by December 25th. Making this an excellent stocking stuffer, assuming you don't get a bad device. (If you do and OnePlus decides to be jerks about it, you can always file a PayPal complaint and they'll fix things for you. Apparently that's what people have taken to doing when OnePlus gives them grief and sure enough it seems to work.)
If you're interested in buying this "flagship killer" you can do so here.
It is far from a bad device, at the price (16 GB for $299 and 64 GB for $349) it's basically a steal. Shell out the extra $50 for the 64 GB model, you'd be an idiot if you didn't.