I'm just about to jump on the HD-DSLR bandwagon here (with a 7D), and for now, a tripod is good enough. But just enough isn't really going to sit well for long, so I'm planning on also getting support rigs.
I have the Chrosziel 450 based system that I've been using for quite a long time with my HVX200. By changing the mounting plate with a few screws and some spacers they have, all of my gear was adaptable and worked great. Their stuff is not cheap, but if you have a number of other cameras they are adaptable and can use the same follow focus, matte box, and in my case a large number of Tiffen filters.
I bought the full Redrock Cinema bundle for my EOS7. It is a great value but has a few issues. First of all, the assembly instructions are on Vimeo, not printed. It's nice but printed instructions can be handier. Second, the MicroArm broke after a couple of weeks of use and the side doors on the matte box kept falling off. Fortunately Redrock has excellent customer service- fixed them without issue. They also seem very interested in customer feedback for improving their products. The matte box uses 4x5.65" filters, which are less common than the 4x4 variety, although you can use masks to enable the use of 4x4's. Finally, the carbon fiber support design is strong and light but unbalanced and obstructs the camera's hatches and controls. I have been steadily removing parts so I can get to the camera more easily. Fortunately it is very easy (and kinda fun) to modify. Redrock also makes a ton of accessories and adapters to customize your rig almost any way you want.
I would recommend calling them to discuss your needs before placing an order- they're good folks.