Advice on acquiring / constructing Dice Towers
The primary goals of a dice tower being

Keeping the dice on the table
Improving the randomization by reducing the ability to manipulate the dice.

There are several good designs, however, the basic principle to check for: it should have at least 3 slanted faces, and all the slanted faces should be covered in felt or corduroy. Friction is your friend, here.
The shape is almost always an L. Let's compare it to a cowboy boot...

The toe is opened up so that you can see the landing zone. It needs about a 3/4&quot; to 1&quot; high rim.
The heel has a slanting plate, angled to kick the dice out to the toe.
The shaft of the boot: deflectors.

Plates: The shaft has anywhere from 0 to 5 angled plates within, usually about 30° to 45° downward, angled to toss the dice about in the tower. I don't use ones without at least 2 additional plates. Most have a top plate, angling down to the front, and a second plate below angled down to the back. The plates should cover about half to 2/3 the cross section. Better designs may have left and right angled plates, or even a narrow center triangle, to toss the dice side to side.
Dowels: if plates are too much trouble, dowels can be used instead. The dowels should be about 3/8&quot; to 1/2&quot; hardwood, and are placed in levels. Top is usually a front to back and a side to side cross, centered. 1.5&quot;-2&quot; down, 2 off center parallel; a crossing set another 1.5&quot; to 2&quot; down. Taller ones may have additional crosses, or even run dowels corner to corner.


Plastic, Foamcore, Bare Wood, Felt, or Corduroy? What do I cover the thing with?

only the inside of the tower and the tops of the deflectors need covering if you opt to do so, and dowel deflectors can have slipcovers rather than glued down ones.
Bare wood is noisy, and some dice will slide flat along it. It's acceptable, but not preferred.
Felt: cheap, easy, reduces noise, no nap, so it produces less hang potential than corduroy.
Corduroy: has a clear nap. This will help catch and tumble the dice. The nap, however, should be arranged to put the lines at a downward angle of 20°-40°, so that the dice also get some sideways motion and better tumble. Probably the quietest of the mentioned materials.
Bare plastic: extremely noisy, very slick. Least tumble.
Foamcore: as slick as plastic, but not as noisy, but often puts more bounce on the dice. A foamcore sole of the boot can easily result in dice bouncing OUT of a low toe. (personal experience.) Also, damaged by water, unless sealed with paint or glue.



There is another design for a dice tower I've seen used: spiral staircase. Each stair was angled 30° down, and it went clockwise with 1/4&quot; drops off each stair. Being bare wood, it was rather noisy, but it also was very random.
Plans &amp; howto's
The plans at http://www.instructables.com/id/Making-a-Formboard-Dice-Tower/ are decent enough; it's a short 2 deflector boot-style.
http://www.boardgamegeek.com/filepage/13307/dicebox-pdf
Plans for a 2 deflector tower. Annotated.
http://www.io.com/~beckerdo/games/articles/HirstDiceTower/HirstDiceTower.html
Building with plaster molded &quot;stones&quot;.
http://webspace.webring.com/people/xc/crosstowngames/crosstowngamesdicetowerplans.pdf
Another set of plans for a square boot.
http://www.io.com/~beckerdo/games/articles/DiceTower.html
A square castle design, using 3 deflectors.
http://www.geeknews.net/2008/01/02/very-cool-diy-dice-tower
Spiral path in square tower; wood core with polycarbonate sides.
commercially made towers
http://www.chessex.com/dice%20accessories/Dice_Accessories.htm I have one of these! It's noisy as a monkey house. But it's good and random, tho' it lacks side-to-side deflectors. the toe plate is a little short, however. Also, it's friction fit, so it can be taken down and stored flat. This is great for the GM on the go... unless you space where you shelved it!
http://boardgamegeek.com/image/625539/gruumsh
the same clear boot after adding some felt to the deflectors...
http://www.bluepantherllc.com/BP3_DT.htm
Kits to construct both small and large dice towers... just need &quot;... glue, rubber bands and about 10 minutes...&quot; The mini is a &quot;land in drawer&quot; mode, and the larger ones are a variation on the boot.
http://www.uniquedicetowers.com 
Assembled dice towers started on Kickstarter.
Alternatives to the tower
The dice tray: a dice tray of some kind (we've often used the box lid) controls the dice, but doesn't add much to the randomization unless requiring a bounce off the back wall.
Dice Cups: all the material issues for towers apply to dice cups. Plus, as dice stacking displays show, it's possible for the skilled to manipulate them pretty well, tho' it's still MUCH harder than in a tray or tower. It does, however, take some practice to shake-flip-slam so that the dice don't roll across the table. Again, good ones are felt or corduroy lined (my good one is). An inepensive one can be made by taking a soup can (not a poptop, tho), carefully filing the edge smooth (steal your sister's emery boards!). Then line with felt or corduroy, gluing it to the inside. Use some more, or some inexpensive leather, to cover the outside. This gets you a lunch and a dice cup for under $15...