We have had great luck with 1/4" round polyurethane belting from Fenner Drives.
You can see it (and purchase it) from MSC
Here is the catalog page:
http://www1.mscdirect.com/CGI/NNPDFF...4587&PMCTLG=00
We use the 1/4 " orange belting...look at the Fenner Drives stuff..
You weld it together yourself ... do a search on CD for round belting and you will get good info on doing this... we purchased a $250 kit from Fenner Drives directly and HIGHLY recommend using it on your system