Caboose Industries O-Scale ground throws. We have a bunch of them and they've worked great.
One caveat, though is they should be placed on the straight leg of the turnout lest they get hit by low-hanging long cars (Gunderson Bulkhead container cars, MTH Amtrak SuperLiners). We actually got one sheared off by an MTH SuperLiner. They're pretty easy to replace if that happens, though, so you should keep a couple of spares on hand.
