Seiko Instruments offers the new fast SLP 450 one-label-at-a-time printer.

The Seiko SLP 450 prints a label in about 1s. Seiko added 2D barcode printing and improved network connectivity to its new label printer.

With a resolution of 300dpi you can print bar codes for storing, shipping or inventory tracking, text and graphics for labeling office files or cabinets, logos, name-tags and more.
Seiko Instruments Smart Label Printers are compatible with Windows 2000, Windows XP, Mac OS 10.2 and higher, Power Macintosh G3/G4 and iMac.
The SLP 450 will be available in May at an estimated street price (ESP) of $189.
More details on the Seiko Instruments site.

See also the Dymo LabelWriter 330 Turbo which prints a label in 2s. That was back in 2004 the speed record.