Here’s an interesting bit of advice for printing directly on blank playing cards. It would be useful for better-looking prototype games.
Cardmaker is a tool for using CSV files to easily generate cards for your games.
Lately, I’ve taken to making cards for units in my games, rather than putting it on on sheets of paper. Having the cards cuts down on table clutter and makes it easier for players to find exactly which unit info they need.
Epic Slant Press has an article on the lessons they learned from their Kickstarter game. I found it to be interesting for the insight into the game industry.
If you’re designing your own games, here’s a page with some pdf, ai and psd templates for playing cards of various sizes. I’ve taken to making unit cards rather than roster sheets for players to keep track of information in my games.