CFFORM has a cool sample of a slush control, basically two selects where you can send items to the left and right. This was designed by Ron Pasch from Prisma-IT. I took his code and packaged it up into a nice little custom tag. You can now have this control on your form without any modification to your cfform tag. You simply add:

<cf_slush name="users" query="#data#" valuecol="id" displaycol="name" colwidth="150" size="5" selected="3">

View Demo

You can download this code here. (I'll be adding it to My Tools in a few minutes.)