The three best uses of ThankYou Points are:

Transferring to Singapore miles to book Singapore Suites

Transferring to Singapore miles to book United First Class to Hawaii
Transferring to Etihad miles to book American Airlines flights

Singapore Suites
Singapore Suites is inarguably one of the nicest First Class in the world.

I just booked myself an award from Los Angeles to Santiago, Chile in Business Class for 35,000 Asiana miles + $24. United would have charged 55,000 miles for the same flights!

Why Asiana Miles
Asiana has really cheap awards to Europe and South America and really expensive awards elsewhere.

Award space is wide open in Turkish Airlines Business Class between the United States and Europe for four people per flight over the heart of the Summer.

This is amazing news because normally award space over the summer is the toughest to find, finding four seats on the same flight in Business Class is almost unheard of, Turkish flies to more countries than any other airline, and you can book the space for as cheap as 40,000 miles one way with no fuel surcharges.
Turkish Routes
These are Turkish's routes to the United States.

From Istanbul, there are great

United 903
Honolulu (HNL) – Tokyo (NRT)
Depart: 11:50 AM on Saturday December 26, 2015
Arrive: 4:00 PM on Sunday, December 27, 2015
Duration: 9:10
Aircraft: Boeing 747-400
Seat: 13J BusinessFirst (United confusingly calls Business Class "BusinessFirst." The real First Class is called "Global First.")

Because I was flying international Business Class, I had free access to the United Club, which is right above Gate 8, the gate we were using, at Honolulu International Airport.

I left the United Club at about 11:15 AM, ten minutes after boarding started.

American Airlines, United, and Delta all release several co-branded credit cards with various benefits, bonuses, and fees.

I have attempted to summarize the following cards on one table for easy comparison:

Some credit card offers in this post have expired, but they might come back.

Update: Below is my bonus offer. This is a targeted bonus, so yours may be different.

Through December 18, 2015, United is offering a 100% bonus on purchased miles. The size of the bonus depends on the number of miles you buy, with the largest 100% bonus kicking in at 30,000 miles purchased.

United miles normally cost 3.5 cents per mile plus a 7.5% tax, bringing the full price to 3.76 cents each.

United is releasing an unusual amount of award space to Europe for Summer 2016. A lot of flights have 9+ award seats in Business Class on the same flight. Book now before it disappears!

United award space can be searched on united.com, and the Saver award space can be booked with any Star Alliance miles.

In October, I booked what might have been my favorite award ever: a Three One Way award that would allow me to see Pohnpei, Palau, and the Philippines while flying the Island Hopper. Read about it here.

Alas, something came up, so I can't fly it. I decided to just fly directly to Japan instead, but that still left the thorny issue of how to turn my old award into an award to Japan.

United charges $200 to cancel an award and re-credit the miles.