I'm a few days behind on these, but I haven't seen them reported at any of the papers or blogs, so:
RP Mark Corey - You remember him from his stints with the Pirates in 2003 and 2004, and from being on the 40-man roster during the Rule 5 draft debacle in November 2003. Corey played for Indianapolis in 2005, then had a mediocre year for the Yankees' Class AAA affiliate in Columbus in 2006.
RP John Riedling: Riedling, 31, came up with the Reds organization and pitched 200+ forgettable innings for them between 2002 and 2004. He pitched in the Marlins organization in 2005 and stunk it up for the Cardinals' AAA team in Memphis in 2006. He pitched only 18.2 innings before the Cardinals released him. He'll be roster filler in either Class AA or AAA for the Bucs.
RP Brandon Puffer: By my count, the Pirates will be Puffer's tenth big league organization. That includes two stints with the Astros and a year in the indy leagues. If you remember him, it's probably from the passable 69 innings he pitched for the 'Stros in 2002. He hasn't really pitched well in Class AAA since 2004, so don't expect to see him in a Pirates uniform this year.
RP Mike Nannini: Nannini, 26, is a former hot prospect from the Astros organization who finally pitched well in Class AA for the first time last year. He'll probably be in the Altoona bullpen.
1B Randy Ruiz: Ruiz, 29, has proven that he can pound Class AA pitching. However, he's a huge dude, he's had substance-abuse issues, and according to WTM, the Royals released him last year because they worried that he'd be a bad influence on their top prospects. As WTM also points out, he'll probably head to Altoona... to play with the Pirates' top prospects.