Your options are basically CAT-5/6, fiber, wireless, or HDSL. You don't mention what sort of budget you have but I'll assume it's not great. PVC is a great conduit and definitely recommended wherever you can lay it. If possible, consider hiring/renting a ditch witch to dig a narrow line across the paved road, which can easily be repaired.
Copper Ethernet is obviously the simplest solution, and the easiest to interface with any existing equipment. The biggest drawback is the distance limitation, though there are ways around this (look into Long Range Ethernet). Daisy chaining each switch to the next isn't ideal, of course, but shouldn't cause any problems provided you can make it between buildings without exceeding the 100m limitation too much.
Fiber is considerably more expensive and probably exceeds your alloted budget, but effectively negates any distance problems. Rugged fiber is available (again, at greater cost), but conduit is recommended. Keep in mind you'll most likely need media converters or GBICs to interface with switches in each building.
Wireless may be problematic as you note, because a mostly clear line of sight is needed. However, this is proportional to the length of the shot, and may still be doable to some buildings.
If there are preexisting phone lines run to a building HDSL is definitely something to consider. You can pick up a pair of modems for a couple hundred bucks and effectively transform one or two phone lines into a ~1-3Mbps Ethernet line, up to a couple miles.
