We have dark hardwood floors and the ceiling is about 13 feet tall.

It's beautiful! I don't know either but maybe just a frame?
I like it as it is tho.

That is a beautiful wall. You might want to add maybe a mirror or, if you want a painting/drawing, look for something with white frame. The actual painting/drawing should have mild colors..I would probably go for a drawing since anything else that has color will clash with your wall

This has a bit of green so I think it would go nice,,if not,,something black and white,,a charcoal/pencil drawing

I be it took him hours to paint that wall! Wow, I love the color combination. Now your job is to quiet it down a bit. I'm feeling something white or light, even grey, without a lot color. Abstract or possibly a large black and white photograph.

No art…a great console table.

Love the wall! Possible add-ons I'd consider if that gem were mine:
* single large, bold, black & white "graphic" with a non-matching frame (create a little tension);
* quad or grid of pen & ink line drawings or black & white photos of a single subject;
* single or multiple framed silhouettes;
* 3-dimensional mount (resin/faux white taxidermy, curly manzanita branch or driftwood spray painted neon/hot color or left in natural state).

SUCH a great wall!

I love the idea of a black and white photograph or a large mirror. We have an open floor plan so we can't do anything too extreme!

I agree with JudyG that all it needs is a console table. The wall is the art.

A vertically hung row of small pieces on the side walls. Pick pieces that require close viewing, which is a different experience than viewing the wall. Use frames that match the lines of the painted wall in color and width. A whole series of polaroids marching up the wall with some little etchings thrown in. Images that make you smile, to be happy you are home. If the space is tight in the apartment (hel-loooo, apartment?) you could put 4- 6 inch vertical mirrors that abut his wall and expand it into the room, even on the ceiling, Should you choose the side images, they could start to migrate onto the wall over time as it feels right. I would focus on landscape and seascapes based on the colors of the wall and in juxtaposition to the clean lines of the wall. Below is a snapshot, un-photoshopped or made prettier, of my bathroom collection. If it took so long to paint, why cover?

The dining room table is next to the wall so it isn't possible to put a console table in

I also like the idea of a mirror... round in shape, as a juxtaposition to the high, graphic grid style of wall design, which by the way is amazing!

something large & sculptural like letters

Here are a few pictures that I found that I think might work in your room! Also a square collection on that wall would look awesome. If you like the pictures just let me know, also there are many other ones too! (:

We also need art for the bedroom but that should probably be a different discussion.

How bout some frames ( with nothing in them?) The wall is pretty busy, so another idea would be a large,framed mirror. It would then have a center focus and you would probably both enjoy the painted wall even more. Even walls can be " anchored."

First-timer to these discussion forums, & increasingly ardent adhere-er to Morris's "have nothing you don't know to be useful & believe to be beautiful", so dismiss or consider my comments accordingly. If considering:
I. having seen a little more of the dining area (love the space, Matt!), I'd add to my prior considerations:
A. a visual nod to the clear/acrylic nearby, maybe:
1. a trip to Tap Plastics to see if I could piece-together a sizable "sculpture" of clear-glued, overlapping, random salad-dinner-serving platter plate-sized acrylic discs or rectangles (suspended from ceiling or mounted on black blocks that "disappear" into the black on the (fabulously!) painted wall;
2. a purchase or creation of a sizable white-framed "floating" frame with a central white ground allowing wall to appear between art & frame, through surrounding glass "matte" (on that central white ground, I'd big-handwrite or computer-generate a quote or Bible verse that inspires, collage a few cut-out, big black letters into single word big (maybe "nourish"), or collage kids' artwork, anything all (recently found $50 13x29 floating frames on clearance at Target for $7 & am digging the look & versatility)); &
B. a purchase of a shallow-ish chunky "lipped" picture ledge or flat shelf (Ikea "Lack", or Pottery Barn "Holman" (currently on sale) for display or function (large white serving platters & vases, found objects, various framed art united via a single colored frame or matte, etc.); &
II. having seen the bedroom (dig the grey-red-cream color combo), I'd consider:
A. I.A.2. above,
B. I.B above,
C. furniture or accessories that introduce "industrial" metal via rivetted aluminum frames, galvanized letters, wine barrel rings mounted "as is" or rigged to frame a central object (& if room were for my young adult daughter, add onto that an ever-so-slight/subtle element of cream-colored softness via burplap, eyelet, or the like).

Inspired by y'all...grateful.

I would look for something vary minimalistic and light with a simple frame. That way the wall and the picture would not compete. Allowing the darkness of the wall to frame the picture.

Try a very long horizontal narrow mirror, nothing else.

Have you thought about a solid abstract in white, cream or one of the complimentary colors on that wall? I would break up the pattern on the wall with a huge 50 x 50 or larger painting or an oversized framed mirror; the floor to ceiling type.

I like Alisia Leeke's idea. I have a piece of art I put in a grouping once and the one I looked at the most was the all white relief impression.

How about a nice large mirror?

I think a mirror detail would be best! I think that a chunky black frame it possibly a black gilded frame could be great. The bulk/chunkiness of the frame will serve as a break accenting the mirror but not detracting from the fun wall detail!