The only way I can think of right now is printing them out on normal paper, cut them out, and then gluestick them onto cards. But the last time I did that it was a mess, and it was too hard to shuffle without them falling apart.
Because of this most of my finished games I have done with pencil and pen. However I am aiming for the ability to make many idenical copies, and having them look nice.
How do any of you go about this?
Well, my inkjet is capable of printing directly to cardstock (at least, the cardstock I have), so I do it that way, although admittedly the cardstock I'm using isn't as thick as I'd prefer (you can still see slightly through them).
Another option would be to take your computer files directly down to Kinko's or some similar copy place and have them do it. There's a nominal fee, but if you're that far along in development, it's not too much of burden to invest in a nice, professional job.
Although, I have done the "cut and paste" method before, to some degree of success. What I did was print the normal paper source cards slightly smaller than the cardstock destination cards, and made sure I glue-sticked all the way to the edge. This made sure that the edges of the normal paper stayed on the cards and didn't curl or peel. I still have to be careful when shuffling, but it works well enough for a prototype.
Hope that helps!