I don't have a lot of TMNT stuff, I do really like the action figures. I don't have any of the originals (sadly I got rid of them all when I got older) but I did buy all the current ones and I have them all on my shelf. I also have the TMNT Lair LEGO, the Shellraiser LEGO, the Kraang Lab Escape LEGO, and Shredder's Dragon Bike LEGO. I have all the movies also. I have all the issues of the current IDW series (the first 13 are in graphic novels otherwise TMNT #1 would be on the top of my list). Probably the coolest TMNT thing I have is the Giant Leonardo PEZ dispenser. It stands approximately a foot tall and plays the theme song from the cartoon when you open his mouth. I don't have any candy for it sadly. It is probably the coolest thing I have because I don't know of anyone else who has one. I would love to get any of those Funko things to add to my collection... That Leonardo is especially awesome.
Okay, after listing all of that, I have a lot more TMNT stuff than I originally thought I did.