Best kept secrets in tele lenses?

I actually just picked up an Oly OM Zuiko 75-150 f/4.  It's fully manual, of course, and it's not the fastest lens in the world, but the zoom range works really well on MFT, and mine seems to be pretty good optically.  $45 from KEH plus an $8 adapter from Amazon.

I'm also considering a used 200 or 300 f/2.8 if I can find one at a good price - there should be some legacy lenses available for less than $400 that would fit the bill, I think...