1: Cut your texture in half and switch them. Just rectangle marquee the left half of your texture, cut it, then paste it. Now move your freshly cut left texture and move it all the way to the right (staying within the textures original borders) then move your right texture to the left. Flatten the image and use the clone tool down the middle (there will be a VERY visible seam) and soften it up or something. Now do the same steps as above, except cut the texture horizontally so you'll have a top and bottom piece. Repeat the cloning and you'll have a semaless texture.
2: Copy and paste a piece about an inch from the left. Flip the piece horizontally so that it's reversed. Move that piece all the way to the right and clonebrush the seam until it looks even.