The trend around here is to give Visa, Target or Sports Authority gift cards. Around here, you can pick them up in your local grocery store. That way the birthday kid can go out and get that expensive sports gear, the video game, or whatever he wants.
I at first thought it was tacky - no thought put into it. Then my kid got a couple hundred dollars in gift cards (an average of $10 - $25, mostly $10 and $15 in gift cards). Was he ever excited to go shopping for that one expensive thing he really wanted.
And then a homemade card. The kids here LOVE to make cards for each other. The sillier the better.