What you get depends a good deal on your budget. I linked two buildings approx 1/4 mile apart with 802.11g wirless bridges from Buffalo Tech, and apart from a clunky web interface, they've been flawless through the New England winter (they went live in October and haven't been touched or rebooted since). I was worried about the brand, but it's been great. The whole kit, including wires, antennae, bridges and power over Cat5 kit was $900 total for both ends. (not counting install labor & masts)

Bridge
Antennae
Power over Ethernet
Coax Cable (the shorter the better)

You'll need masts too, but you can get those at Radio Shack.

The shorter the Coax the better, signal losses accrue with length. That's why the Power over Ethernet - my routers are up in the rafters and I didn't want to pay electricians to put outlets up there. The POE modules are plugged into the UPS at my patch panels/hubs at each end.

Oh yeah, laser pens are handy for aiming as are a pair of FRS radios (Motorola Talkabouts etc...).

You'd probably also want a grounded sheild someplace between the two antennae at the 'elbow' to prevent sideband radiation from one antenna interfering with the other.

My result was 1.2MByte/second throughput in either direction. The data is encrypted at the bridges and they only answer to eachother. I don't remember the encryption details...I'm sure they're on the BuffaloTech website someplace.

YMMV, of course! Good luck.

-Zeke