OK, it’s sloppy markdown (it’ll look better on github), but here’s a table I compiled from the site linked above (includes reports from the comments). I’ll add more hardware as info becomes available. I haven’t had time to fill in some missing info for some setups, and some of the spots I took liberty to fill out may be inaccurate (like an ssd labeled as flash etc)… any suggestions are welcome. Note uX=usbX, aX=usbX sata3 adapter:
* Raspberry Pi3b(+) USB Boot Compatibility
Type--|--HDD--|--Adapter--|--Boots?--|--Reboots?--|--Boot/reboot requirements--|--Notes--|--Reference
a3ssd--|--Crucial BX500 240GB--|--Orico USB 3.0 to SATA 3.0--|--Y--|--Y--|----|----|--https://community.home-assistant.io/t/hass-io-transfer-from-sd-card-to-ssd-or-usb/97452/11?u=truglodite
a3ssd--|--Kingston A400 120GB SSD (SA400S37)--|--Startech USB3-SATA3 adapter (USB312SAT3CB)--|--Y--|--Y--|--bootcode.bin--|----|--
flash--|--Kingston Data Traveler 100 G3 32G--|----|--N--|--N--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Kingston Data Traveler 100 G3 8G (DT100G3/8GB)--|----|--N--|--N--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Kingston DataTraveler 2GB (DTI/2GB)--|----|--Y--|--Y--|----|--Slow--|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Kingston DataTraveler G2 4GB (DTIG2/4GB)--|----|--Y--|--Y--|----|--Slow--|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
a3SSD--|--Kingston SSDnow uv400 240GB ssd--|--ICY Box IB-AC603L usb3 adapter--|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Lexar 64GB USB 3.0--|----|--Y--|--Y--|----|--http://www.staples.com/Lexar-S45-64GB/product_2071237--|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Lexar 8GB JumpDrive S50--|----|--N--|--N--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
uHDD--|--MeCo 16GB USB 3.0--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
a3SSD--|--MyDigital 128GB SSD (MDMS-Sbe-128)--|--GungHo Labs USB adapter--|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
u3ssd--|--MyDigital 512GB SSD--|----|--Y--|--Y--|----|--ran hot--|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
a2ssd--|--"OCZ Agility 2 2.5"" 60GB SATA3 SSD"--|--Ebay USB2 Enclosure--|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
a3SSD--|--OCZ Vertex 30GB--|--NexStar USB3 enclosure (NST 21053)--|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
u3flash--|--Samsung 128GB USB3 (MUF-128BB/AM)--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
uHDD--|--Samsung 32GB USB 3.0 drive--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--SanDisk 16GB Cruzer Glide (DCZ60-016G-Q461)--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Sandisk Cruzer Blade 16GB--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Sandisk Cruzer Extreme 32GB (SDCZ80-032G-G46)--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Sandisk Cruzer Extreme 64GB (SDCZ48-064G-U46)--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Sandisk Cruzer Fit 16GB--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Sandisk Cruzer Fit 16GB (SDCZ43-016G-GAM46)--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Sandisk Cruzer Ultra 32GB (SDCZ48-032G-U46)--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
a3SSD--|--Sandisk SSD Z400s 128GB--|--Manhattan SATA-USB (130103 aka Super Top M6116)--|--Y--|--Y--|--bootcode.bin--|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
uHDD--|--Toshiba Canvia Basics 1TB--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Transcend 3.0 32GB USB stick--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
flash--|--Transcend JetFlash 32GB (TS32GJF510S)--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
a3ssd--|--Kingston 120GB A400 (SA400S37/120G)--|--Vantec USB3 2.5" SATA (CB-STU3-2PB)--|--Y--|--Y--|----|----|--https://community.home-assistant.io/t/hass-io-transfer-from-sd-card-to-ssd-or-usb/97452/21?u=truglodite
flash--|--Verbatim Pinstripe 16GB--|----|--Y--|--Y--|----|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
???--|--WD 1TB PiDrive--|----|--Y--|--Y--|--early versions need timeout--|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
???--|--WD 314GB PiDrive--|----|--Y--|--Y--|--early versions need timeout--|----|--https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
Since there are many flash drives on the list, I want to remind folks that a usb flash drive will be pretty much as failure prone as an sd card since they both use NAND type flash memory. There is really no point in moving from an sd card to a usb flash drive, other than it may be easier to access physically when it fails and needs replacement. For this reason, you should only look at ssd drives on the list.
[edit: @godinperson, since you got it working would you mind sharing the details of the hardware you used… so I can add it to the list? Thanks!]