i've just been skimming so forgive me if these have been noted before (i did do a search, but...)
i paint with baby oil to make things transparent (the paper becomes kinda waxy, almost like, er, wax paper. [or vellum]). i got the idea after noticing the transparent-like quality of splatter marks in my cookbook. cooking oil doesn't work so hot, but baby oil does. i like painting only part of the paper to expose certain key words or images.
i only have a few examples handy, but i assure you this is fun:
(rose paper painted and pasted over music)
(text printed on tissue paper and painted)
i also like to print on tissue paper. i trace the edges of a piece of cardstock with a glue stick and gently lay down a piece of tissue paper. then it's easily run through the printer and easy to detach (since you only paste around the edges). i like to do layers. i'll use photoshop to create different colours or patterns and then stack the pieces of printed tissue paper.
on this one, you can see how i didnt get the tissue paper perfectly lined up. but it gives it a kinda fuzzy cool look, i think.