Tokina 80-200mm f/2.8, Canon EOS/EF mount. Beast of a lens, you could just about use it as a billy club. Came up on Craigslist, guy was selling off pieces of his Canon collection to finance a 5D MkII upgrade. I had watched a couple pass by on eBay and decided his $400 asking price was reasonable. We met, I tried a few back-to-back shots against my 70-200mm f/4L at f/4 and fixed shutter times, and the results were close enough that I bought it and popped the f/4L on to pay for it. All expenses considered, it was a break-even purchase.
So far, I'm reasonably impressed. The only thing that hinders this Tokina from being an ideal acquisition is a breathing front-focus with a rotating front element, and the AF is on the slow side. I'll live with it for now, as having a constant f/2.8 minimum aperture is worth it to me, and I don't have $1100 lying around for a Canon f/2.8L. Here are some quick test shots that I fired in my kitchen, using Aperture Priority and a card-diffused 550EX flash, all at 800 ISO on a Canon 40D. These are 1900x1425 crops from a 10MP image, resized (at a very slight quality loss, of course) to 1024x768 for convenience. There is otherwise no post-processing:
At 200mm f/2.8, it's definitely running soft, but IMO not unreasonably so. At f/4 (as noted) things have improved greatly, and by f/8 it's pretty much peaked. So far, performance outdoors seems consistent with these results. Here's an 800 ISO, 200mm f/5.6 shot with mild PP. Foreground is at a distance of about two miles, background mountains are about 5-6 miles distant, lighting is dusk:
Long-term performance remains to be seen but given that the alternates run in the $700 range (Sigma, Tamron) or $1100 on up (Canon), this looks to be a reasonable budget piece for someone whose hobby is not yet generating income. It also sharpens up slightly below about 150mm or so, and the minimum aperture is a respectable f/32.