RouterBOARD 532 for APs and 112 for client ends. Use CM9 radio cards as they can do both 2.4GHz and 5.8GHz, have a good output power and receive sensitivity and are very reliable.
There is a weatherproof metal case option for these which includes pole mounting hardware and is very rugged (it's also nice and small).
There are also weatherproof RJ45 connectors available, these are handy as you dont have to open the box to connect anything once you put it on a mast.
Antennas will depend on distance and area you want to cover. Rootennas are cool for client sites but invlove a small amount of work getting everything mounted inside.