There are so many out there that I just limited myself to analyzing those that are small enough and made of metal so they can fit on your key ring:
Kingston SE9 G2. I've been using these for quite a while and unfortunately for USB 3.0 they aren't super fast at 30MBps read and 10MBps write, but convenient. $22 for 64GB. No reason to get less anymore 🙂
Sandisk Ultrafit. This is small and doesn't have a key ring, but it is incredibly fast at 140MBps sequential read and 40MBps sequential write, so pretty incredible performance and just $25 at Amazon
Transcend JetFlash. Smaller than the Kingston and about the same speed but it is also waterproof?!