Cards cost way too much for a piece of folded paper with writing on it, so here's a quick, easy alternative.

What you'll need:

Paper, get the same number of pieces of paper as how ever many cards you need.
Stamp & ink pad (optional)
A pen.
Colored pencils or crayons.

Step 1: The Cover

First you'll need to take your piece of paper and fold it in half. Then take your stamp and stamp it right in the middle of the front. Carefully, so you don't smear the stamp, take your pen and write in bubble letters whatever your giving the card for- Merry Christmas, Happy Holidays, Happy birthday, whatever. (If you don't know how to do shaded bubble letters just go to this other instructable How to make and shade bubble letters

Then you can draw a background to your stamp, if you want.

Step 2: The Inside: Part 1

First draw a wavy oval on the side of the card you'll see when you open it. Then draw several more until it looks something like the picture above. Then write a small note, if you want you can make the first letter of his/her name bigger. Then, on the other side of the card, put your stamp again and write a small motivational phrase around it.

Step 3: The Inside: Part 2

Here's where your crayons or pencils come in handy. Color your scribbly rings in one color, and then color the half-page around them another. If you need to know the coordinating colors here's another link.The color wheel

Pick a color on the color wheel and the color directly across from it on the color wheel is the one that would look best with it. For example: Orange colors look good with blue, reds look best with greens and so on. Then color the other side of the card as desired.