I have almost the exact same setup - though your wall looks wider than mine - and I went for the MASH Studios LAX Series Wall Mounted Desk with vintage crates mounted on the wall above (with French cleats) for books.

Its not the clearest overall picture but you can kind of see the setup here: https://www.dropbox.com/s/53kqkwily2idtv7/DSC_0124.JPG

Ikea makes a new desk that seems like it was designed to go under your desk: http://www.ikea.com/us/en/catalog/products/80221352/

It doesn't provide much storage however. Maybe a low storage cabinet stored under the lowest part of the stairs would work, so that it doesn't add too much visual clutter.

A OneLessDesk would look great there.

http://hecklerdesign.com/OneLessDesk/

I've always though this guy's desk under his stairs looked great:

http://www.flickr.com/photos/nycgraeme/2287826242/

Something minimal and spindly.

Pilsen from Crate & Barrel: http://www.crateandbarrel.com/pilsen-48-desk/s575286
Portica from Room and Board: http://www.roomandboard.com/rnb/product/detail.do?productGroup=19633&catalog=filter&menuCatalog=room&menuCategory=213&menuSubcategory=146
Flat Bar Desk from West Elm: http://www.westelm.com/products/flat-bar-storage-desk-g126/?pkey=coffice-desk-chairs

You could also just go with the black-brown expedit like we did.

I think it would look best for you to put one unifying table top all the way across the space. Too many elements will only look messy. Mount a counter directly to the wall at desk height. Then put some IKEA Stolmen storage cabinets underneath on the left side, leaving the right side open for sitting. Take a look at how chezerbey did their loft office - I think this would be a good solution for you (with the storage cabinets under the desk).

http://chezerbey.com/tour/loft-after/

Asian-style tansu or matching dressers that can look like tansu. The one that would be at desk height could be the actual desk in matching style. The minimalist look of tansu works very well with the minimalist architecture of your unit.