Commercial cards are well and good, however don't forget the creativity of yourself and your gamers. Have your gamers draw items on 3x5 or 4x6 index cads on the non-ruled sides. Don't guarantee they will ever get to use it personally, but allow them to participate in the creative collaboration a great game is. Do specify they use color fast inks. If you want color fill, I find prisma color and spectra color pencils work well and can be blended using a simple drafting shield and velum eraser for rub mixing. I request the player provide the drawing with an initial and a date. It's really fun when I pass out one of the really old cards in a treasure. The drawing may be crude, but the history gives it a 'feel' that commercial cards can't match. I do sometimes scan in cards for possible re-use if it's a drawing I feel suits a common item. A good ink-jet or laser printer with card stock capability helps <G>.
I require cards to be turned back if the item is lost. stolen or destroyed. The better ones get recycled later and add to the feel of the game. I've also been hard nosed and ruled that a player who was careless and actually lost several carded items was 'thieved'. Smart players in my world have been known to photo copy their carded items! That way if an entire game folder is lost I can allow the 'clone' items back in, if I feel the player just had a real accident. Items become tangible, and I allow players to trade items that are not magically attuned or locked to them.
Another fun thing with card creation is if you participate in a multi-GM environment, you can do joint development. Years ago I used to sit down with a table full of GM friends and we'd all bring stacks of blank carded items. The usual rule was to pass items around the table, each GM adding a power, materials description or item history. Some items only would get a couple of powers and we'd call them done. Others became significant artifacts. Then, based on our plans for campaigns, we'd horse trade the cards. I'd never leave with all the cards I started with, and I'd frequently get ideas for good sub-plots.
In fact, it's brutally fun for GM's in cross world set ups to scatter a set of cards that get special powers in conjunction with each other across several worlds. Makes for the epic quest!
If you decide you want to do something similar, I suggest setting ground rules for card marking. Codes for 'User automatic', 'always on', uses, trigger-able by, charges and standardized damage nomenclature all help.