My go-to ink for fabric stamping is Versacraft. It's a pigment ink and it's permanent if you iron it once it's dry (does fine in laundry if your item is something that needs washing). It comes in little cubes as well as full size pads so it's possible to get a range of colours without having to dedicated a lot of $$$ or storage space. You can see the colour range here
Tsukineko has also introduced something called "All Purpose Ink" - last time I joined in a thread about fabric stamping somebody mentioned this as they'd seen it demoed at a show. I haven't used it but it sounds interesting. Details here
on the Tsukineko site.
The reason Stazon says "not for use on fabric" by the way is that the solvent base may attack some fibres over time (so I was told when I e-mailed Tsukineko and asked about it a couple of years ago). So I guess the bottom line is it's probably OK to use for something that isn't intended to last for years!