Following are some links to places that sell useful materials, tools, etc. I don't own stock in any of these companies, nor can I warrant their performance will be excellent. But I've had good luck with them so far. There are many, many more than these.
Makers of force sensing resistors.These are useful as touch sensors, providing a variable resistance depending on how much force is pressing on them. You can order them via email: firstname.lastname@example.org. They are available as .2 inch circle, .5 inch circle, 1.5 inch square and a 24 inch trimmable strip. Prices are about $5 each, with a minimum order of something like $65. Check it out. They sometimes will send samples.
This is an electroluminescent fiber, about 1/8" in diameter, that looks kind of like neon, but is flexible and can be run off batteries. Available in many different colors. Tel. 718-544-4400, 1-888-LIVEWIRE, Fax 718-575-3668. No email!
This is a place in California that sells surplus electronic goods. Tel. 1-800-826-5432, Fax 818-781-2653.
I just got their catalog, haven't ordered from them yet, but they have a lot of good prices and a wide selection. This is in Ohio. Tel. 1-800-524-6464, Fax 800-524-5414.
"Incredible Stuff, Unbelievable Prices" is the motto of this wacky store in Chicago that sells surplus everything. Tel. 847-982-0870, Fax 800-934-0722.
This is a place in California that sells new electronic goods, with many useful kits and components, including computers and parts, as well as sensors. Tel. 1-800-831-4242, Fax 800-23- 6948 International Fax 650-592-2503.
This is a place in Minnesota that sells new electronic goods, with a very complete selection and a thorough on-line catalog in the form of pdf documents. Many sensors also available. Tel. 1-800-344-4539, Fax 218-681-3380.
This is a place in Florida that sells surplus electronic goods, sometimes wacky stuff, lots of power supplies, motors, some sensors. Good prices. The phone operators have nice accents and call everyone who phones, "Honey." Tel. 1-800-625-6733, Fax 800-432-9937.
This is a place in Nebraska that sells surplus electronic goods, transformers, pneumatic and hydraulic cylinders and valves, motors, some heavy duty. Good prices. Tel. 1-800-488-3407, Fax 402-474-5198.
This is a place in California that is much like Surplus Center. Good prices. Tel. 1-800-325-9465, Fax 626-796-4875.
This is the leading source for just about everything electronic in Germany. They have an interesting array of sensors and microcontrollers, too, and ship overseas, as far as I know.