Tritton See2 Xtreme USB Video Card

Pros: Works on Macs.
Extended desktop with 19" and 22" WS LCDs on my Mac Mini.
Good resolution.
Good support.
Supports rotation, of at least one monitor at a time so far, on Macs. Say they are fixing this.
If you can't afford a Mac that supports extended.

Cons: Display arrangement limitations not worked out yet.
No documentation for Macs yet.
Has some resolution issues with different sized monitors being used at the same time.
Computer off, connected monitor stays on desktop image.

Summary: It solved my Mac Mini display limitations.

I am waiting for this to be out of basically a beta version for Macintosh and get full support for Macs and allow complete arrangement of both monitors so I can have both in portrait mode.
I like that I can have different slideshows on each monitor.
Love that I have an extended desktop.

The phone support is toll free and very helpful (as much as they can be at this stage of development for Macs).
Small footprint. Easy to setup.
Great for us monetarily challenged Mac users.

I used a script called Screen Span Doctor, if I recall the name correctly, on my eMac before it died, and that guy hasn't written one for the Mini. Yet, I hope. It worked flawlessly on the eMac and was free. If i had the money I donate it to him just to get him to write for the Mini.

Paid too much ($109 ) at Microcenter, but I could take it back immediately if it didn't work. But it does, mostly, to my happiness.
I would recommend this to anyone that needs or wants an extended desktop that can't because of whatever limitations.
Supposedly supports up to four monitors. Haven't had the opportunity to try that.