We went with the Closetmaid system (from Home Depot). It is wire shelving, but really like the options/flexibility for change.
Did not want to spend thousands and this was fairly reasonable.

The system is very flexible with the use of the rails and the brackets that can move as your requirements change.
On one side of closet, I did shelving (for sweaters etc) with another portion for hanging clothes. The opposite side has various hanging space.

This set-up works very well for me. Total cost was @ $500-600 if I remember correctly. Still need to do DH's closet (so I can have some of his space too, LOL:))

One thing I really wish I had was some space dedicated for shoes. Most of mine are stashed away in another cabinet.
All depends on your needs though...

DH and I are handy, so we just built our own. We share a closet and each side (his & hers) has double hanging space, 3/4 hanging space with shoe shelves above, and full length hanging space with a shelf above. The back wall is all adjustable shelving that we share. I use linen-covered boxes for undies, socks, etc. that would otherwise go in a dresser.

It's all birch plywood with cypress wood trim. It took us a weekend to build and install and ended up costing about $400 in materials. The boxes and extra shoe hanger for me were another $40 or so.

I am an Elfa fan. We have done a number of closets and when we built this house, I used the builder stuff everywhere but our MBR closet. I was ready to feel all guilty, thinking that the "regular" stuff would be just about as good as the Elfa, but in fact, it turned out to be pretty inferior. Elfa does go on sale (at The Container Store) a couple times a year and we drive to get it to save on shipping. We have bought the basics and then added as we needed/could afford. We even pulled a few closets out of one house and reconfigured them for new spaces. It's very flexible and portable.

Even if you don't use Elfa, there are lots of pics on the website for ideas...

Here is a link that might be useful: Container store

I am also a big fan of Elfa-had one before and want one now! We used a local carpenter to do most of our closets. Just be sure you know what you need when you get true build-ins as they will not adjust. For grown ups it may be ok but for kids I prefer the adjustable stuff.

My walk-in came with the house. The builder used bull nosed pressed wood AND cedar to line the sweater cubbies. The cedar is key!
{{!gwi}}

You'll probably get a lot more info over on the Organizing forum. I recall reading good things over there about Easy Closets, but I have no personal experience with it other than testing different configurations on their website. That's a pretty handy feature even if you choose a different system.

Here is a link that might be useful: Easy Closets website