I have the cheap plastic ones from Wal-Mart. The bottle and holder came together for about $5. I have one mounted on the seat tube (the frame, not actual seat post) and one mounted hanging on the underside of the top tube. That one seemed a little precarious with the extra weight and length of the Costco bottle, so I put a mini-bungee cord around it to help hold it in. I hit a lot of rough pavement bumps and it has never fallen out of the holder.