The biggest problem with conductive paints and inks is that they crack and loose their conductivity on fabric because the surface of fabric is porous and uneven. To print on stretch fabrics is an even bigger issue that might be resolved by combining the paints with flexible materials such as latex, silicone or fabric mediums. Painting on fabrics can lead to some nice results regarding stretch and bend sensing.
Also see: Tutorial on painting paper circuits
CuPro-Cote from LessEMF is highly conductive and great for painting circuits. See above tutorial.
CuPro-Cote >> http://lessemf.com/paint.html (USA)
Have not tested the following copper liquid paint:
There are a range of carbon based paints available. While these are not as conductive as the copper one mentioned above, they are ideal for painting sensors.
YShield from LessEMF >> http://lessemf.com/paint.html (USA)
SPI Supplies >> http://www.2spi.com/catalog/spec_prep/cond_paints3.shtml (USA)
EMFields >> http://www.emfields.org/screening/paint.asp (USA)
Pens containing silver ink. See: Conductive Pen
Maplin >> http://www.maplin.co.uk/Module.aspx?ModuleNo=36275&doy=17m4&C=SO&U=strat15 (UK)
This company produces silver and carbon inks for electronics and screenprinting.
Manufactures two silver screenprintable inks designed for flexible substrates.
Make your own conductive paints and glues!
By mixing conductive powders/pigments or particles with paintable mediums you can make your own conductive paints. You want to use a medium that will shrink when it dries rather than expand, bringing the conductive particles closer together, rather than further apart. Graphite powder is easy to buy as lock lubricant, but is relatively course, finer powders make better connections. I would recommend starting by making some samples. Mix as much conductive material with your medium as possible, before your medium is saturated and turns clumpy. If this is conductive, then make more samples with varying ratios, until you achieve the right result for your purposes.
!!! With latex i observed that the conductive material sinks to the bottom and the latex forms an isolating layer on top of them. So that, when you measure for conductivity it appears that the cured mix is not conductive, but if you measure from the bottom, or use needles to probe into the mixture, then you can read values.
The following links contain instructions on making your own conductive paints and glues: