Yeah, I'll break down the ones you can use.
The ones you can sell for TC are the ones where you enter a PIN code, like PSN Cards, XBox live, Steam e.t.c.. In most cases they send the items/tc first and then you send them the PIN.
The ones you can't are ones where you need to go the cashier and have them swipe it. Those include everything from gift cards(Wal-mart, Zellers, e.t.c.) all the way to movies.
If you're looking to sell a sporting goods card, chances are it won't be possible. If it's from a place like Nike or Sportcheck I know that you need to bring those to the cashier. So no, you wouldn't be able to sell it, unless you were willing to mail it to the person, which most people wouldn't do.
Offtopic side note, I started the rave about selling PSN Cards, XBox Cards and stuff a couple weeks ago. :>
Your welcome.