I used 350gsm matte paper for my cards for its strength and durability. Perhaps in the future I'd also try some glossy paper - although I'm generally against the look and feel of glossy stock, it'd probably hold the ink better than matte.
Though I originally wanted the cards to be bound by a screw at the top left, acquiring such materials at late notice just wasn't going to happen. I subsequently experimented with bulldog clips and methods of temporary binding to allow the cards to be taken out and used like flash cards.