@Adam
I like the colorchoice on the first screenshot. Subtile / bright fonts on the front face and the backside is using colors similar to the background of the screenshot.
@ Xerra
If you want to have some coding fun, your cards could be slightly animated.
This is from my halloween compo entry "Trick or Sweets":

To achieve that effect I had:
- a background
- an overlay (the "grungy/torn paper"-look)
- a "stripes" image
- the actual image (in that case the lollipop)
drawing was done this way:
- draw background
- set handle of stripes-image to "center"
- set rotation to "(360 * Millisecs()*"slownessFactor-eg.-0.1") mod 360"
- set blend to shade blend (or use low alpha on alphablend)
- draw stripes-image
- reset rotation, alpha, ...
- set handle of actual-image to "center"
- set scale "0.95 + 0.05*sin(Millisecs()*"scaleSlownessFactor-eg.-0.05")"
- draw your actual image
- reset scale
- draw overlay on top
The overlay can eg. be used to slowly fade out to the background etc.
What is all the fuzz about? it removes the "staticness" of the game - it adds a tiny bit of movement. Might not be worth the hassle but if properly done I think it can increase the visual attractivity.
Nonetheless I would really want to see a revisited look of your cards - take Adam's suggestions into consideration. Especially colors need to suit together in the base configuration - it attracts or distracts people right on start. If you need any "PSD" for card design, kindly ask and I (or maybe others like Adam) might create you some stuff.
bye
Ron