TL;DR: Get the Hikeren
I have three different cheap ELM327 Bluetooth models that work with FORScan (the 3rd one was a surprise because it's kind of a POS). They were all purchased from Amazon (links below) and prices are current as of the date of this post (price in parenthesis is what they were at time of purchase). These work on Android and Windows devices, but like many other Bluetooth products, they don't play well with Apple iOS (due to Apple's incomplete/crappy implementation of Bluetooth).
1. BAFX Products 34t5 Bluetooth OBD2 Scan Tool for Android: $21.99 ($19.99)
The first one has been mentioned already in this thread. It supports more protocols than the others, but it is larger and more expensive (although still very affordable). I used the BAFX in my 2011 Mazda MX-5 for more than a year, leaving it in and on all the time, and other than protruding down into the footwell a bit, it worked great. I have also used it to troubleshoot cars belonging to several friends as well. It pairs and connects quickly and stays connected without issue.
2. Hikeren Mini Bluetooth OBD2 Scan Tool (with power switch) for Android: $11.99 ($9.99)
While the BAFX did not protrude down far enough to interfere with driving (in my car, YMMV), I did find myself bumping it when getting in and out, so I decided to give one of the tiny ones a try. The Hikeren was around half the price of the BAFX, and it has a power switch, which I don't bother using (never had a battery drain issue with either). When reading reviews the tiny ones seem to get the brunt of bad reviews, but this Hikeren model has performed flawlessly for me. Like the BAFX it pairs and connects quickly and stays connected. Unlike the BAFX it is so small I can't imagine it getting in the way in any vehicle. However, if your OBD2 port is recessed, it might be hard to remove later.
3. Vgate Bluetooth OBD2 Scanner for TORQUE APP ANDROID: $9.99 ($6.33)
The third one seems to be popular. I see it recommended on various forums a lot, but reviews of this product are not confidence inspiring. On Amazon 26% of the reviews are only 1 or 2 stars. If you consider 3 star reviews unfavorable, then a full 33% (one third) of the reviews are poor. This one was actually given to me by a friend who wasn't happy with it and bought a BAFX on my recommendation. I fully expected this one to fail with FORScan, but it works. It is really slow pairing and connecting, and has, on occasion, dropped the connection. Although it seems to work, I can't honestly recommend it, even for the lowest price I've seen it at (it was $3.96 in January). The others above are simply worth the extra money. Also note that the one I have does not exactly match the picture, so there are at least a couple of different products being sold as the same thing (all labels and markings are identical, but the plastic case and interior layout is slightly different).
Click for image of what FORScan Lite says about these adapters in my car (no that's not my real VIN).
Notice that the Vgate (right) has significantly more delay time than the BAFX or Hikeren (which had identical information in FORScan Lite). 15ms vs 36ms. This confirms what I experienced when using it. The Vgate is sloooow.
According to the documentation I have been able to find, all of these devices support the following protocols:
SAE J1850 PWM (41.6Kbaud)
SAE J1850 VPW (10.4Kbaud)
ISO9141-2 (5 baud init,10.4Kbaud)
ISO14230-4 KWP (5 baud init,10.4 Kbaud)
ISO14230-4 KWP (fast init,10.4 Kbaud)
ISO15765-4 CAN (11bit ID,500 Kbaud)
ISO15765-4 CAN (29bit ID,500 Kbaud)
ISO15765-4 CAN (11bit ID,250 Kbaud)
ISO15765-4 CAN (29bit ID,250 Kbaud)
In addition, the BAFX also supports:
SAE J1939 CAN (29bit ID,250 Kbaud)
CAN (11*bit ID,125*Kbaud)
And finally, here are my three OBD2 adapters (quarter for size comparison):
I hope some of you find this information useful.