Yeah, there's two that I know of - tototek's pce-pro and neo's pc-e flash cart. I don't own either, so I won't vouch for their quality or usability.
I've had both so I'll give you my opinion:
Basically, avoid the Tototek cart. It's ugly, fragile (no proper casing for the cart) and highly complex as it uses a combination of USB and parallel ports to generate its power and transfer data. Add in the fact that it only holds 32MB compared to the Neo Card's 64MB, as well as the fact it costs $150 to the Neo Cards $110, and it's not worth considering. Not incidentally, the after sales support on the Tototek site is dire.
As for the Neo Card, well, all I can say is that I think it is excellent. If you have Windows XP, then it's the ultimate choice for those that want to play the whole Hu-Card back catalogue on real hardware. I've got Volfied, Out Run, Alien Crush, Raiden and Xevious plus quite a few others on my flash cart. I can even load up the special 3 minute tournament versions of Gunhed and Soldier Blade, just for a laugh. Neo cards are the same size as standard Hu-Cards, and are very professional looking. Mine has an R-Type logo on it, and it looks great.
I'm a player, not a collector, so I'm not interested in having the game boxes etc. Saves space too. For the equivalent of £55, I can play any Jap Hu-Card I want, and it's so easy to use. I recommend it to anyone that can afford the initial outlay - it pays itself off in the end, that's for sure.