I've had pretty good luck with Tokyo Aquatic; they have stems and pots in addition to TC cups. Ordered from them several times with no issues.
Also no problem with the one order I got from Liquid Creations, and you can buy single stems for pretty cheap if you are looking to experiment with a bunch of varieties at once (I only ever ordered stems from them though, so I can't speak either way as to the quality of their potted plants).
There are several aquarium plant sellers on the big auction site who have pretty good reputations and also guarantee no snails. I have purchased probably 60% of my plants that way; the key is to find vendors who guarantee their product quality and cleanliness, order one just plant the first time to see if it's up to snuff, and then return to purchase more from the ones you know are worthwhile.
I'm not a giant fan of TC cups myself, so I look mostly for pots/stems too. I've used TC plants before and probably will again because it's often a challenge to get certain species any other way, but my experience has been that they are much harder to transition than more mature plants, plus they tend to be a bit expensive relative to plant size.