There are others,that was just the first one that came to mind.

There are ones out there that mount to the seatpost collar and skewers. Problem Solvers also makes a binder with rack eyelets.

You can find the p-clips at many bike shops or you can look for cushioned p-clips at a hardware store. Either will work.

The Tubus clips are universal and will work with any rack. I've used them for the upper and lower attachment on mountain bikes and road bikes with Delta racks, Sunlite racks and Tubus racks. They work for all of them very well.

re: "Are seat post (beam) racks really terrible?"

my 2 cents ... yes

Oh yeah I forgot about those. I might pick up one of those and use a regular rack in conjunction with P-clamps for the bottom attachment only.

I actually use this as we speak to carry lunch, clothes, any small items. The one I use is the Carbon beam rack with a carbon post and a topeak trunkbag. but have the beam rack maybe 1/2 inch away from the post clamp. I also replaced the bolts with titanium to lighten the load. Works flawless and I am the envy of my commuting area with that rack on my system six. Rack never moves and is crazy light but strong. I once had a quick release rack but they move all over the place and are too bulky for a road bike.