I have used two rulers to make a TIS unit. The Tri-recs works great, but I also love the Deb Tucker V-block trimmer. You can see her demo video on youtube. The advantage of the Tri-recs is that it is available at Jo-Ann and you can use a coupon. If you can't pick up a specialty ruler before you need your quilt finished, there are some excellent suggestions above that should help you. I'm basically lazy and a gadget nut, so I like to let the rulers do some of the work for me. :-)
Darren