I have used this and loved it....
http://www.blockcentral.com/hst/hst-3inch.pdf
This is the easiest way for me to make (HST) half square triangles...she has 4 sizes to choose from. They come out just great and no bias sewing.
I sew "just outside the dotted line - closer towards the cutting line" to give a little leeway and have had great success with the block sizes.
Good luck
lol ... the above reply is pretty much the same thing...she just typed faster, lol :-P