I use the Hitachi 6gb microdrive.
The downside to this card is it eats the battery faster, so a battery pack of some sort is almost always needed. The other downside is, it doesn't register time right. I have to leave dummy files on it to get the available space below 4gb's before it'll show the proper remaining time on the card when I'm recording. A bit of a pain in the ass.
I'd say the card is reliable tho, the mt on the other hand....I'm starting to notice more things about my problem the other night at moe tho. When I was recording and not getting any levels, its because the mt switched back to the factory defaults. I didn't notice that till Saturday night tho. Looking at the MT again yesterday, it should have been obvious this happened, because the filenames started over from 34 back to 001. I guess thats a sign.
Why the recording stopped half way thru the second set tho, I'm not for sure. I'm pretty sure it safe to say that its not the card though since it was just over half full.
But yeah, the 6gb hitachi works nice and is cheap.