Sulky Sticky Fabri-Solvy Stablizer - sold by the A4 (US A4 size) single sheet.
Not the cheapest product but this stuff is amazing. Pop a sheet in your printer, print it out, peel off the backing then stick to your fabric ready for stitching. It does away with the need for lightboxes, tracing paper etc etc. It's really good for complex designs. Once you've finished stitching just leave it to soak for a few minutes - it washes out completely. Just make sure you are using colour fast threads!
You can just draw directly on it if you don't want to use the whole sheet in the printer - just cut out the bit that you need and save the rest for another project. I use it to make stitching on t-shirts easy - it's also good for embroidering on denim as other transfer methods don't work very well (iron-on pens for example don't show up on denim).
The only downside I have found is that your needle tends to get a bit sticky as it passes through the Solvy and fabric. A fix for this is Thread Heaven if you are lucky enough to have some (they've stopped manufacturing this amazing product). Instead I have a bottle of nail polish remover handy and a cotton pad and run my needle over that every now and again.
Shipping charges apply to this product.