Usually 650nm & 670nm Class I & Class IIA
http://www.barcodesinc.com/pdf/Symbol/ls7808.pdf
http://www.barcodesinc.com/pdf/Metrologic/ms9520.pdf
Everyone I've seen has been 1 mW or less, but many of the older ones were HeNe tubes.
EDIT: When the grocers went to handheld scanners, these things popped up everywhere. I was moments away from snagging one on at least three occasions. They are a little more difficult to come by now, since there have not been any real upgrades to UPC scanners.