In reality you don't even need that. Here's the tools you can get by with:
Tape measure
Hand saw (not electric or anything... just a good 'ol hand saw)
Drill (or screwdriver if you want to be uber cheap, but trust me... you'll want to use a drill)
1 & 1/2" wood screws (nothing shorter than this, but can go up to 2")
Sand paper
Optional tools:
Circular saw
Wood stain + paint brush
Belt sander
K.I.S.S. (keep it simple stoopid)
Just screw one wood board into the other (see picture below). Don't try and do fancy dovetails or any of that other stuff. If you find screws REALLY unsightly, you can try pre drilling holes and using pegs, but personally I find pegs to be a pain and a bit less stable if you don't do it right.
Depends on your budget. Fancier woods will look better without having to stain them, though they might be harder to cut. Personally, I would recommend just some 1x6" thick pine wood boards. This will give you the easiest build and the most flexibility.
This is an example of a couple of things I've built with the same concept on all of them. The bookshelf on the right is just one long piece on the sides and all the shelves are cut to the same length and screwed in from the sides (2-3 screws on each side for each shelf). Depending on your decor, you can leave in the natural wood color or you can go buy some wood stain and go to town. There's plenty of different shades to choose from. The only other thing to figure out is the backing. I forget what it is called, but there is some kind of cheap sheet of particle board that you can find at home depot/lowe's/etc. that you can simply cut to size and nail into the back of your finished structure. You can also stain it to match the rest of the shelf.
Quick word of advice- If you are going to stain, make sure you cut all the pieces to size and then stain it. Don't wait until after it is all assembled to stain it or you'll miss lots of little corners. Just an FYI.
PS- To answer the question about screws not showing, if you use the black colored screws and stain the wood a darker color, the screws will blend in and you can't really see them.