Letus is well known for the Letus Extreme; a lens adapter that lets you attach a 35mm lens to "traditional" video cameras like the Sony EX1 and produce much shallower Depth of Field. Now they are coming out with products for DSLR users, including a viewfinder and rod supports, and they now have a specific website for their DSLR products: http://letusdslr.com/
Letus Hawk DSLR Viewfinder
Constructed of carbon fibre with a 2.75x view factor and +1.5 to -2.5 Adjustable Lens. The viewfinder has 3 lenses in 2 groups, a removable eye cup and a camera plate for mounting.
It's $385 @ Amazon though it's not expected to ship until early June.
LetusDirect: Letus Hawk DSLR Viewfinder product page
Letus Talon K1
A quick release baseplate, stainless steel L-bracket, and 90mm stainless steel rod extensions which are female threaded on each end. Intended for use with a viewfinder, it can also be purchased with the viewfinder as the Letus Talon K2.