Blizzard is now offering a new twist on the Recruit-A-Friend program. They want you to send out invitations to your friends who used to play WoW, but have canceled more than 90 days ago. The offer is for a 10 day free trial of the Burning Crusade. If they accept and become a paid subscriber, you get a free month of Warcraft.
You can have up to 5 invitations out at once and each person has up to a month to reply before the invitation expires and that slot opens up to you to send out another.
This is pretty smart, IMHO. We've all known guildmates who have disappeared since the summer began. If they've been thinking of coming back, at least you can get a month free subscription out of it. Check out the FAQ for full details.