I love the 30, 60, 90, Triangle. You don't know how many uses it has when trying to do an isometric drawing of a house. A 30 to the left a 30 to the right a verticle line, and you've started an isometric drawing. I don't remember what the 60 is good for right off hand though. If I had to do a drawing I'm sure I'd remember.
Now the 45, 90 Triangle, not as useful as you might think. It has them, but I prefer the 30,60,90.