It's kind of a disease! (an enjoyable one, but a disease nonetheless)
Spray starch in a can is a total rip-off, and way too expensive! So, what are the alternatives? (That one itty bitty bottle of Best Press was $6.95!!)
I like to use liquid starch (Sta-Flo, to be exact), and make up my own in a spray bottle. It's nice to be able to formulate different strengths and not have to go buy a new can every time! I've found a good balance is just a little less than a 1:1 ratio. (This is the same stuff I've used to soak partlets and petticoats, and anything that needs a stiffer starch set)
Starch is amazeballs, but when you need a nice press set, without all the starchiness (for example, pleats in silk; a spray bottle of about 1/2 white vinegar, 1/2 water totally does the trick. I've not had it stain or spot anything (yet), and it gives a nice crease and set to things without the crunchiness of starch. (Don't worry, the vinegar smell dissipates quickly - you won't be walking around smelling of pickles!) Kind of works the same as Mary Ellen's, but way cheaper, though not as nice-smelling. (and in some respects, works better, I think!)
Pressing cloths are amazing - use them, love them. If you don't have any yet, I would suggest starting to collect some out of scraps or stash - at least 1 canvas/duck, 1 muslin, and 1 silk organza. White is the best - no fear of colors bleeding. Making a pressing cloth is the easiest thing in the world - just cut out a piece of fabric (about 12"x12" or so) and zip around the edge with a serger or zig-zag. (Here is a great list of the uses for different types of pressing cloths)
Inbetween starch and pressing cloths is something called a 'Rajah Press Cloth'. It's supposed to set in/take out creases in poly and poly blend fabrics. I don't use mine very often, as I don't use poly very often at all....but just so you know, it's out there....
A neat trick is to slightly dampen the press cloth (with straight water, or water/vinegar) - it gives kind of the same effect of using steam from the iron, but is a lot more gentle.