Custom furniture's not really so custom -- typically, you're merely picking from fabric swatches that'll all eventually turn one of the many shades of Ray's. For a higher level of individualization, try Imuri Designs.
Imuri will take any piece of furniture you own/shamefully "rescue" from the sidewalk and emblazon it with a Pop Art paint job. The process: you bring in a table, chair, cabinet, lampshade -- even the box where you keep your gimp -- then specify the level of customization. You can opt for basic patterns/designs Imuri's already worked out, or create your own masterpiece -- anything from a vibrant pattern of your choosing, to a portrait of your face for a chair (a joke which'll keep self-respecting guests from staying long enough to sit). Before setting to work, Imuri'll create a mock-up, ensuring that the life-sized Kim Jong Il you've commissioned for your credenza doesn't come out looking like you with a sweet perm and oversized women's sunglasses.
Imuri's not limited to furniture, and if you own your apartment, they'll come in and give the same treatment to your walls -- giving lustrous depth to the base coat you've somehow managed to turn a whiter shade of pepperoni.