i am a fan of simple shelf rails, the kind that you clip the supports into and place the shelf anywhere on them. I got mine at Home Depot, but pretty much any store like that carries them. While you are there, purchase some cabinet grade plywood (or any wood that is 3/4" thick that you like the look of) and have them cut it to the sizes you want for your shelves.

If you are nice to the person cutting it, and tell them what you are doing with them, they will be real careful with their cuts and do a nice job. All the cuts may not be free, but they will be straight. :) 

Stain or paint or polyurethane, whatever color you want them to be. You can use two rails, or three for shelves at alternating heights that overlap, or four, or... Only limit is your imagination.

 Another great shelf is the Lack shelf at Ikea. It is a floating shelf, which means you don't see any of the brackets that hold it up, it's like magic. :) We have a few, they are nice for all sorts of places. Even makes a good mantle. 

I found a few interesting ideas... it all depends on what look you are going for. Ladder Bookshelf for the rustic look... Staggered shelves are fun and more modern... and the secret hidden bookshelf door is probably not what you are looking for, but it's interesting none the less!

 On top of all that, I have a bit of a bookshelf "fetish" (I own a lot of dvd's) so I'm constantly tagging bookshelf ideas on my delicious page.

 Hope this helps! let us know what you go with.

what look are you going for? here's some DIY instructions..... but you could always get the same look with shelves......

as far as easiest goes.......get some laminate shelves and use large hardbound books stacked on their sides to create the height that you want, be sure to only go a few feet high with this otherwise it might get to be too unstable. 

instead of books, you could also use interesting wide-mouthed vases that were the same height, or brackets (practical and decorative) to hold up the shelves.