St. Louis Cardinals at Pittsburgh Pirates

Baltimore Orioles at Pittsburgh Pirates

The Orioles and the Pirates celebrated the 40th anniversary of the teams' 1971 World Series appearance.

Pittsburgh Pirates at San Diego Padres

Both teams dressed in 1978 throwbacks, the Padres in the mustard and brown outfit they've worn a few times in 2010, and the Pirates in a nice looking pinstripes jersey over black pants combo with the yellow pill box hat.

Pictures are screenshots from MLB.TV and Cox 4 San Diego:

Pittsburgh Pirates at Oakland Athletics

The A's defeated the Pirates 5-0 on 1970s Turn Back the Clock night. Both teams wore flashy uniforms from the 70s, with the A's in bright yellow and green and the Pirates in black and gold. Pittsburgh even dusted off its famed pillbox caps, although their yellow ones shouldn't have had stars. The Pirates and A's were dominant teams in the 70s, combining for five World Series titles.

Pittsburgh Pirates at Detroit Tigers

Another Negro League matchup, as the Pirates dressed as the Pittsburgh Crawford(s) again, and the Tigers were again the Detroit Stars.

Cincinnati Reds at Pittsburgh Pirates

For the second of two consecutive nights, the Pirates honored the 30th anniversary of their 1979 World Championship teams with games against the Cincinnati Reds. On Friday they wore the gold-over-black combo, and on Saturday they went with the pinstripe combo. The Reds also wore "polyester-pullovers with sansabelt pants" from that era. Read about in the UniWatch Blog here.

Cincinnati Reds at Pittsburgh Pirates

For the first of two consecutive nights, the Pirates honored the 30th anniversary of their 1979 World Championship teams with games against the Cincinnati Reds. On Friday they wore the gold-over-black combo, and on Saturday they went with the pinstripe combo. The Reds also wore "polyester-pullovers with sansabelt pants" from that era. Read about in the UniWatch Blog here.

Detroit Tigers at Pittsburgh Pirates

As mentioned by BurghFan in the comments, the Tigers and the Pirates commemorated the 100th anniversary of their meeting in the 1909 World Series.