Macrorie, I went through the process ages ago when I decided to move up from 35 mm still. After a lot of thinking and making a pest of myself I settled on 6x9 (in the U.S., 2.25" x 3.25", 2x3 for short), looked into all options. I ended up with a 2x3 Pacemaker Speed Graphic, later got a Century Graphic (bargain version of 2x3 Pacemaker Crown Graphic). I also got an one of the Ensign 820s as recommended in this thread by Ian Grant; he and I disagree about 820s and the 105/3.8 Xpres, I wouldn't recommend either. And more recently, in geologic time, I was given a 2x3 Cambo View Camera.
My present 2x3 kit contains my original 2x3 Graphics (Pacemaker Speed, Century), the gift Cambo, and assorted bits to make a Cambo view camera that will accept my lenses on 2x3 Pacemaker Graphic boards and a 6x12 roll holder, and many lenses (35 mm to 900 mm). You can read about my adventures with lenses for the Graphics at http://www.galerie-photo.com/telecha...2011-03-29.pdf . I don't like fixed lens cameras, find them limiting.
Along the way I tried to build a "Baby Bertha" long lens SLR around my little 2x3 Cambo, assorted bits, and a 2x3 Graflex RB Ser. B SLR. That project was a catastrophic failure. Read about it, if you're interested, at http://www.galerie-photo.com/baby-bertha-6x9-en.html