The companies I have used in the past are:
Fabric on Demand
I was very satisfied with both and depending on what you are looking for, one might work better for you, but check them both out.
My plan is to send the same design to several of the manufacturers using their requirements and post a blog on the results.
A new (to me) print house is Modern Yardage. I heard about this site in the Elizabeth Busch workshop I recently took at the Visions Art Museum. From the comments made, this is also an excellent option for your custom fabric design.
Be sure to review all the criteria for submitting your artwork to each vendor. They do differ and must be followed precisely for best results. All the printers offer a variety of fabrics in different weights and fiber and even papers (Spoonflower) that they will print on. All offer a swatch service for a minimal fee so you can make sure you have the correct colors before ordering your final yardage.
Modern Yardage requires TIFF file format, RGB or LAB color—Because of quality issues, we do not accept CMYK colored files and 200 dpi resolution. The image must be sized as it will be printed. They will not scale custom files.
Fabric on Demand accepts .jpg, .tiff, .png, .psd, .ai, .eps, .pdf. Maximum 300 dpi to allow enlargement and minimum 72 dpi at actual print size.
Spoonflower accepts formats in: TIF, JPG, PNG, GIF. The file must be less than 40MB (150 DPI recommended)
Advanced Digital Textiles are a little more expensive, but there are many options of types of inks, dyes, fabric finishes, etc. These choices might be exactly what you are looking for. You can order a complete 5 x 5 inch swatch set of all their base fabrics for only $12.
SC Fabric Printing will work with you from any type of sketch or digital design you submit. They have a wide range of fabrics and pricing depending on the print and design services you require. They accept a variety of graphic formats including: .tif, .jpg, .ai, .psd, etc.. They require you to save your files in CMYK at actual size 150 dpi for optimal output.
If you have had any experience with any of these print on demand vendors, please let me know. I would love to hear about your results and opinions.