I've got the old Cactus Jack shirt from when he first appeared in the WWF, but that's so torn and faded at this point that I ordered a new one yesterday.
I've also got the old Stone Cold 3:16 shirt with the smoking skull on the back. I haven't seen (or really looked) for a replacement for that one because the new ones I've found all have that stupid copyright stuff/WWE information underneath the "3:16" part, and that just really ruins the shirt.
I also ordered the Eddie Guerrero "I'm Your Papi" shirt as well as the tribute one. I don't know if I'll ever wear those ones though, I just wanted to have them.
Right now I have the Benoit 4 Real shirt, with the crosshairs on both sides, had to get it because the house show I went to didn't have the Shelton Benjamin shirt in my size...
I've had a couple of Goldberg shirts in the past, and a couple of Stings...I also still have a shirt that has Y2J, Rock, and Austin on the same shirt, and their "logos" on the back, with a WWF attitude logo.