Please forgive my ignorance if this is old news, but after reading about these cheap wi-fi boards, and how easily you can use them with their built in AT style command set over a simple serial link, my mind is buzzing with a lot of very cool ideas. I'm posting a link to one of sparkfun, but as I'm sure most of you know these kinds of boards can be had even cheaper if you shop around. Anyone use one of these yet?
google esp8266
tons of code and examples, well known and well documented.
with the arduino comparable bootloader, they can be programmed with the arduino IDE
also, google wemos and nodeMCU
Old news and in fact there is a new chip, the ESP32, that has more buzz to it these days but the ESP8266 still is a good choice. However, I agree that the possibilities with a $1 WiFi module are exciting. Even more exciting is that you can directly program the ESP8266 using the Arduino IDE. The ESP-01 module is not quite so useful for that purpose since it only has one (?) GPIO pin broken out and doesn't have all the circuitry on the board to act as a plug and play unit but they have nice little boards with the USB circuitry, voltage regulator, and all useful pins broken out for only a couple dollars more. The WeMos D1 Mini is a good board for that purpose. I've done one project with the ESP8266 as a WiFi module running the AT firmware and one project directly programming the ESP8266. I actually tend to prefer Ethernet for communications on my own projects but WiFi is kind of fun to play with and you can actually use the ESP8266 as a very capable microcontroller even if you don't use the WiFi feature.
pert:
Old news and in fact there is a new chip, the ESP32, that has more buzz to it these days but the ESP8266 still is a good choice. However, I agree that the possibilities with a $1 WiFi module are exciting. Even more exciting is that you can directly program the ESP8266 using the Arduino IDE. The ESP-01 module is not quite so useful for that purpose since it only has one (?) GPIO pin broken out and doesn't have all the circuitry on the board to act as a plug and play unit but they have nice little boards with the USB circuitry, voltage regulator, and all useful pins broken out for only a couple dollars more. The WeMos D1 Mini is a good board for that purpose. I've done one project with the ESP8266 as a WiFi module running the AT firmware and one project directly programming the ESP8266. I actually tend to prefer Ethernet for communications on my own projects but WiFi is kind of fun to play with and you can actually use the ESP8266 as a very capable microcontroller even if you don't use the WiFi feature.
Glad to hear someone has put it to use, so I'm going to pick your brain a little. 
My main question is how well you have found the reliable range on those boards I linked with the built in PC-trace antenna. My only experience with these PC trace antennals in the 2.4 Ghz range was with those WIXEL boards made by Pololu. I once did a significant amount of work developing a prototype for a product line using those, and considering I was basically making direct radio links between identical boards with short simple packets of data, I was a bit dissapointed to find that reliable communication beyond about 25 feet was pretty dismal. Of course that's based on not only the antenna, but also the transmitted radio power and receiver sensitivity. At those frequencies my engineering skills are pretty much non existent, so for ready made boards I've kind of learned to ask what actual users have found in real world situations. Granted, if it has a good little TCP/IP implementation, it should be a bit more robust than the WIXEL communication could ever be, but I suspect not by much. So the bottom line is, haw far from the Wi-Fi router have you found it to work well?
Both the ESP8266 projects I did for a friend who is more of a WiFi person. I only tested them on my workbench, which is about 20 ft from the WiFi router. I'm not sure what sort of range he is using them from but he didn't report any problems. Actually I remember him remarking on how strong the signal was for the ESP8266 access point that's used to configure the WiFi credentials so it can connect to the router.
You can get ESP8266 modules or boards with an SMA connector that will allow you to use an external antenna. I can't remember the specific model number of the modules but the WeMos D1 Mini Pro is the board I know of with the SMA connector.
Last summer I had an Adafruit ESP8266 Huzzah (on board trace antenna) running 24/7 for four months about 35 feet from my router, with two or three walls (wood framed with sheetrock) in between. No issues.
I would expect a similar range as a mobile phone has - which also comes with tiny built-in antenna.
https://www.hackster.io/rayburne/esp8266-mini-sniff-f6b93a
get your ESP8266 and load the sketch.
the wemos D1 mini comes in a few varieties.
one is a cheap board no shroud. the chips are surface mounted to the board
another has a castellated mini-board on it, has the full shield
yet another is of the open chip type, but has the antenna as a trace with a socket for an external antenna. you have to cut the trace to use the external antenna.
I would offer that names like D1-mini-pro and V2 and such will help with the search but also that the clones use those words to get more hits and they do not always hold true to the manufactuer.
also, Wemos seems to have become a generic term and clones are printing it on boards that are not official.
if you want to see [distance] what is possible, youtube will show you what some people have done.
if you need distance more than a specific chip, read up on the LoRa devices. prices are all over the map at this point. 10's of kilometers are being discussed.
if you have a farm, a single Arduino at the router with a LoRa and then you can put your LoRa devices anywhere you want.
DaveEvans:
Last summer I had an Adafruit ESP8266 Huzzah (on board trace antenna) running 24/7 for four months about 35 feet from my router, with two or three walls (wood framed with sheetrock) in between. No issues.
Thanks. Much appreciated, and that's just the kind of responses I'd hope for and find helpful. 35 feet in a typical building through ordinary walls is reasonable and respectable with a PC trace antenna. I'd be curious if anyone has gotten further, and at what point they felt the error rate or performance was becoming unreliable. And I realize that all wi-fi routers are not the same, and some will do better with weak incoming transmissions.
I appreciate everyone else's response. As many point out on many threads and subjects, you can "google" specs and manufacturer's claims and get plenty of info about what products "should" do, and you can consider similar products and assume the performance is also going to be similar. But bottom line, nothing IMO is better than real world experiences by folks who have actually worked with a product, and can testify of actual data. Especially with such a cheap item.
Yes, however such real life experiences are anecdotal unless you are looking at a large number of them. Obviously your environment will be completely different than mine, his, hers... the best you can do is get a ballpark estimate and work with it. I can however tell you that I have no problems with an ESP-01 that is about 15M from the router, in another room.
It might make more sense to compare with devices that you already have in the environment, like cell phones, etc.