Oops, forgot about this. Anyway, it's not specific to TCG design, but one of my favorite books on game design in general is The Art of Game Design: a Book of Lenses. It's a textbook, unfortunately, so it has a fairly eye-popping price tag, but it also means that the usual hacks for getting a cheap textbook apply (or look for it at the library; that's where I read it initially).
Since I enjoy MtG, it's no surprise that I'm a HUGE Mark Rosewater fangirl (he's the head designer for the game). He writes a weekly column on (mostly) Magic design. He's been doing so for years, so there's a ton of material. You'd probably benefit from a rudimentary understanding of how the game's played to dig some of what he's talking about, though. He's actually doing a kind of retrospective column right now, which gives you a nice overview of stuff he talks about in greater depth in other articles, plus some occasional links to further reading. He also has a really nice series on very practical issues like how to handle playtesting, creating actual card prototypes, iterating, etc. Other than that a couple of personal favorites are based on talks he gave at his daughter's school," about randomness (re-reading it I see it actually mentions A Book of Lenses lol, I'd already read it by that point), and his post on the "New World Order," some guidelines MtG design put in place to try and control complexity creep in the game. Honestly, there is a TON of stuff here, so just browse around and see what interests you. (Unfortunately the MtG site underwent a recent, terrible redesign that crashed my browser three times just in the course of finding these links for you; do not go browsing if you've got something you fear losing up in a tab.)
I also find [http://www.sirlin.net]Sirlin[/url]'s game design posts useful; he has a fighting game background and a very different focus than MaRo, which I find interesting. A lot more emphasis on balance, which is a separate issue in Magic (development instead of design), so MaRo doesn't talk about it much. The "best of" sidebar is a good place to start, just pick whatever interests you. I guess he doesn't actually make trading card games, but card games, yes.
Those are pretty much the only ones I consistently look at. I'm just a dabbler, really.