Actually, there is only passing similarity between the Su-25 and the A-9A. The Su-25 wing is back-tapered with significant anhedral, whereas the A-9 has a straight, flat and rather thick-chord wing. The Su-25 has much longer and narrower engine nacelles, due to its turbojet (as opposed to turbofan) engines. The fuselage on the Su-25 continues quite far aft of the empennage, with the vertical stabilizer and rudder atop the fuselage, whereas the A-9's fuselage ends with the rudder. Speaking of empennage, the Su-25 has its horizontal tail almost inline with the wings, but with only slight dihedral. The A-9 has its horizontal tail much higher than the wings, with very pronounce dihedral. The Su-25 has a high, stepped canopy as opposed to the A-9's lower-sitting cockpit with the large bubble.
Really, both of these craft are described more by the basic requirements of a close air support attack plane than any similarity to anything else. If anything, both could be said to be simply enlarged and much more rugged descendants of the Cessna A/T-37 Dragonfly.
Now the Buran/Rockwell International Orbiter deal - there's a case of flay out copying. But remember, there's nothing particularly classified about the Space Shuttle airframe. They might have been able to get drawings just by asking for them!
The Tu-2 was a reverse-engineered B-29. Tupolev simply took a few Strats apart that Russia was given by the US at the end of the war, figured out how to make tooling, and put them into production. Even the Tu-95 Bear (and its various sub-types) owe much to Tupolev's access to the pressurized fuselage and thin wing innovations of the B-29.
The Tu-144 bears a much stronger resemblance to the Concorde than it does the XB-70 or the cancelled Boeing SST. The Brits/Frogs were much further along on their SST than was the US, so that's the one that the Soviets were able to copy with mixed success. The recent cooperative venture between Russia and NASA has given us much more insight into the Tu-144 than we could have ever hoped for.
As far as a C-141 clone goes, you'll have to expand on that a bit for me, QCMGR. All of the big Antonov transports that I'm familiar with are pretty unique to the old Soviet Union. There was one that bore a more than passing resemblance to the C-5, but IIRC, it never really went into production, and was used more for publicity and propaganda stunts.
Remember, of course, that the MiG-15 and -17 were powered by first-generation turbojets that were reverse-engineered from Rolls-Royce Nemes engines that were supplied by the Brits much in the same fashion that the US supplied the B-29s.