i am a pro at stacking chess pieces. i am the best in the world (at least i think i am, i cannot find anyone better than me). here are some pro tips:
1) height is not important. having more pieces, and perferably a variety of chess pieces (not just rooks), is far more interesting.
2) stacking chess pieces is not all about building the highest tower or the tower with the most amount of chess pieces. You can also make your stackings of chess pieces resemble something. it is always fun write words or short phrases with stacked chess pieces. you can also make a three dimensional model of a standing up four legged animal.
3) rooks can be placed up-side down on a flat surface. if you are trying to build a tower, one rook, preferably up-side down, should be your base and the only piece touching the surface. if you are a beginner, i suggest you stack all the rooks first before stacking any other pieces.
4) knights can be "hooked" onto the rook. if you hook two to four knights on a rook, you will get a pretty wide and stable platform to stack the rest of your pieces.
5) when stacking chess pieces, it is not necessary to stack the chess pieces in a vertical position. you can make it sideways. actually you have to make some pieces sideways otherwise it will not be possible to stack all the chess pieces.
6) each chess set is different. you do not want to use glass chess pieces. nor do you want to use chess pieces that are heavy on one side and light on the other. you want your chess pieces to be balance and made out of material that will not break if dropped from high altitudes. Some chess sets are easier to stack than others.
7) you will fail often and your tower will fall frequently. do not give up. practice helps a lot. if you find it too difficult to stack an entire chess set, then begin with half half of a chess set first. even i, a pro, had to practice stacking with half of a chess set before i could stack a complete chess set.
my album:
http://www.chess.com/photos/view_album/IM2DZ4U/album-name
p.s. this is why chess is better than poker (no offense poker fans, i love to play poker and i love stacking playing cards. unfortunately, i do not have enough poker decks to actually make something pretty out of it. also, stacking playing cards is too common in my opinion and i like unique and interesting stuff. that is why i prefer stacking chess pieces more than playing cards.).
I don't know about you guys, but when I was little I liked to build towers with my chess pieces, one upon the other. I don't remember exactly, but the tallest I ever did was: the four rooks (upsidedown, normal, upsidedown, normal) a queen (upsidedown) and a king (normal). How tall can you make your chess tower?
PD: Don't use any lenght units for obvious reasons. Also, the tower must hold without support for five seconds at least.