Inkle Loom Pattern Generator - using a fill-in form you can try different patterns with lots of colours and see how it will look.
Master Sett Chart - from Jane Stafford; lists suggested setts for cotton, linen, bambu, silk and wool.
Master Yarn Chart - from Interweave Press; lists many yarns with yards per pound and sett. Free but must register.
Random Stripe Generator - choose colors and width of stripes; intended for knitters but works for weaving
Reed Substitution Chart - figure out how to thread the reed when you don't have the most appropriate reed
Reed Substitution Tool - a simple form from Jane Stafford tells you what to thread with the reed you have
Treadle Reducer - a simple form that helps you reduce the number of treadles a pattern uses when you don't have enough
Weaving Calculator - a helpful tool to calculate your warp and weft yardage, as well as your project costs.
Weaving Color Mixer - terrific tool from Tien Chiu that illustrates how 2 colors [your choice] mix in various weaves