I'll reiterate that without knowing what you plan to do, it's difficult to make any meaningful suggestions. I'll try to generalize a bit, and hope this helps you zero in on a solution ...
Large belt/disk units - these use 4" and wider belts. Lots of large units are available from Grizzly (and many other tool vendors). There are a number of 4" units that show up on CL, even here in AZ and back in OR ... should be plenty in your area. I bought an old Craftsman 4 incher at a local garage sale for $40, and it's kind OK, but shakes a lot. I probably need to replace the v-belt. Haven't used it much yet.
Oscillating belt sanders - these are generally great for woodworking. The spindles are vertical, perpendicular to a largish table, and the belt slowly oscillates up-and-down, so you don't burn a path in it when sanding wood. I used one a couple of years ago. It had about a 3 foot platen and a 6" or 8" wide belt - quite a beast, but it did a great job.
More recently, I bought a used Ridgid EB4424 oscillating spindle/belt sander -
http://www.ridgid.com/Tools/EB4424-Sander/ It's a nice tool. It uses a 4" x 24" belt, backed up with a steel platen. I've used it for both metal and wood. The spindles are, of course, handy when shaping curves (use plenty of talc during setup, to prevent sticking on the cores). Got mine through CL for around $100. Home Depot sells them new for about $200.
Handheld belt sanders - these usually use 3" or 4" belts. I bought a "sanding stand" accessory for my Bosch 3" unit, so it can be bench mounted ... sort of. Not a great solution, but worth considering, as there are lots of relatively cheap used handhelds out there.
Professional belt grinders - these are a mainstay of knife makers. Most seem to use 2" wide belts. They're obviously great for what they do, but tend to be expensive. The October/November issue of
Machinist's Workshop has an interesting article on a relatively inexpensive DIY unit.
Smaller belt/disk units - these usually use a 1" wide belt.
My faves!! I have two Delta units - 1x30 belt/5" disk (model SA150, AKA Grizzly H6070 or Rikon 50-150) and now a 1x42 belt/8" disk (model SA180, AKA Grizzly H8192 of Jet J4002). Both were bought used.
I've never had any great success with the disks. They've got uneven cutting speed across the diameter ... and half the disk wants to lift the work up off the table! So I've converted both to use a Scotch-brite wheel in place of the disk (see post #727 in POTD).
I use the belt very frequently - both the section backed up by the platen (for precise cuts) and the section above (more for blending). The narrow belt width is nice, too. I sometimes use the edge to form notches, undercuts, etc. I generally cut metal with it, but have used it for wood also. Works great with either. And as I said in my POTD post, the Scotch-brite wheel is the cat's meow for deburring, polishing, etc. on all kinds of metals.
AFAIK, this pretty well covers what's out there. Hope it helps you decide what would be best for your work. Once you're there, you can get more specific in your CL searches!
