First, always consider checking out your own local sources for flooring. Big box stores--Lowes, Home Depot, etc., are good sources. Check your local yellow pages for flooring stores as well. You may find what you want and you will generally save shipping costs.
Sheet vinyl would be preferable because it will be seamless. Other options, are individual floor tiles. Installng them in either a one-color floor, or using two colors and installing in a checkerboard pattern are also cool. Home Depot is a good source for ordering floor tiles in a very retro mottled look. Many many color options are available.
If you don't find what you're looking for using the above resources, Marmoleum is available in lots of excellent patterns and colors. It can be ordered and delivered right to your door. Pricy, but beautiful stuff.
Some interesting choices from Tarkett:
Also, Armstrong VCT tile can be special ordered at Home Depot and Lowes. Be sure to ask at the flooring desk to see ALL of the samples as they only have about 20 of them on display and they have hundreds (thank you Tim Heintz). You can go all one color or buy two colors and create a checkerboard pattern!