self-checkin system for GDG São Paulo
See it live in http://luisleao.com.br/checkin/
You need to create a Google Spreadsheet where the first row is the header and the three first colluns are ID (usually e-mail address), name and company (name and company will be printed on label). Only the first sheet will be used.
You can copy and use the model https://docs.google.com/spreadsheet/ccc?key=0AtpnOtM8lIrgdGFWVHc2UkFYTnV1Qy1yZlhlSXQ0Mmc&usp=sharing. Send e-mail confirmations with QRCode. We used Apps Script to do that.
Create your own label downloading the Dymo Label software (http://global.dymo.com/enAU/Software/LabelWriter_450.html).