I recently noticed a fabulous trellis over at Kiss of Sun:
And I think it would work wonderfully for what I want to do with tomatoes this year. I'm going to modify the design slightly, but I love the general structure. I'm going to sink electrical conduit pipe into the ground and create an arch out of smaller pipe. From there, I'll hang hogwire for supporting the vines. This should solve a lot of concerns I've had with other designs and remain inexpensive enough as far as permanent vegetable garden structures go.