In my opinion,
Mikrotik RouterOS on RouterBOARD 500 series. This stuff can take care of the wireless side of things, routing (which is recommended for site to site links), plus VLANS, tunneling and way more if needed. I usually use these with Wistron CM9 a/b/g radio cards, or
Ubiquiti SuperRange series for links over 15km. Both cards have good output power and receive sensitivity and are very reliable.
For antennae I often use
Pacific Wireless aas they are well built and not too expensive. The exact types you will require depend on the layout and range of the network you intend to construct.
I have used this combination sucessfully for several commercial multipoint site links, a hobbyist network and a small ISP. The gear is extremely flexible, but do note with this comes the downside of being more complex to configure than some other pure bridge equipment and the fact in most cases it must be assembled before setting up.
One site I set up a network for previously used Trango wireless bridges. The Mikrotik gear cost less than half the price, runs at three times the speed and has so far proven more reliable.