LicenseKeeper 1.0 will let you type or copy in your registration info, sure -- but it's also prepared to keep track of vendor website URLs, support email addresses, and lots of the other bitsies that tend to go missing when you need them. It will import directly from Mail.app and scan for serial numbers in the inbound registration message (a killer feature if you use Mail; I'm waiting for the equivalent Entourage capability). You can even attach files to the serial number records. A downloadable demo will handle up to five license records and three attachments each before asking you to pay up.
There are two other options for this task that I haven't mentioned so far: a general snippet organizer like Yojimbo or KIT, or a free license tracker like Licensed. Either path might work for you if LicenseKeeper isn't to your taste.
Thanks to those who sent this in.