My solo slacking setup is as follows:
3 x locking HMS biners
15m x 1" tubular webbing
2 x giant slings (each 5m x 1" tubular webbing tied with a water knot)
2 x carpet scraps (at least 50cm x 75cm)
2 x line lockers (single oval links of 3/8" zinc plated stainless steel chain)
The guys at Canadian Tire will be overjoyed at having to cut every other link for you. 1ft of chain will get you about 6 line lockers. Using line lockers allows you to avoid using any knots in the system and also keeps the line flat by bighting the webbing an passing it through the link, then back around on itself and through again. You can then clip a biner to the resulting interior loop instead of using a clove hitch. See
http://www.slackline.com/?p=106 for details (actually the whole slackline.com website is great). Be sure to file down the burrs at the weld on the inside of the link or you will shred your webbing over time.
I tension the whole thing with a 3:1 using just two biners, with the webbing running under itself so it stays secure under its own friction. The tension system should be about about 20% of the length of the span to avoid having the biners touch and being unable to tension it anymore. I can get it pretty tight by myself, although it's easier with two people.
This setup is great for slacklines up to about 25 feet, anything longer than that and you should probably look into a removable pulley system using static cord.
The carpet scraps are
essential to protect the trees and your webbing. Setting up a slackline on a tree without padding will leave big gouges after just one session.