Celtic Web Art and Borders

Tairngire Graphics
The images are free for personal use, though the artist requests that you donate time or money to the American Diabetes Association. There are a variety of ready to use tiles, borders and sets. You can find Celtic Accent graphics, and some lovely Celtic borders.
Long Playing Computer Graphics
Bradley W. Schenck provides a variety of knot designs, gripping beasts, and interlace designs, including tiles and background images, in a Celtic style. Don’t forget to check out his store—there are some lovely Celtic inspired mugs and tiles (and other stuff) for sale. Mr. Schenk has neither slavishly copied medieval manuscripts, nor used scanned in tracings; his is a new take on an ancient style.
VendelCrow Graphics
VendelCrow offers web graphics in Celtic, medieval and Viking styles, including sets and tiled backgrounds. Be sure to read his terms.
Reed’s Celtic Computer Art
Reed Mihaloew offers not only art (various sorts of knots, interlace patterns, and tiled backgrounds), but instructions about creating your own Celtic art, and support materials in terms of bibliographies and background information.
Aon Celtic Art and Illumination
Cari Buziak (who uses the Celtic computer, a Mac) offers both commercial art prints and clothing, and a selection of her own Celtic style clip art and cards, and stich and beadwork patterns as freeware. In addition to some beautiful art, she also offers information and tutorials.
Celtic or Knot
Howard Oliver offers a variety of Celtic inspired knots, graphics, web page sets, borders, arrows, and buttons, free for non commercial use. See his terms. Mr. Oliver makes interesting use of textures in a number of his images.