I would first extend a short 18" deep wall beneath the beam on the left to balance out the room - then have your cabinet-maker devise the cabinets so that there's a reason for the bump-out on the left and balance it out on the right: Perhaps a tall, narrow, solid door for small items on the far left that could be balanced out by a similar door on the far right...

With a bit of planning and creativity, you can accomplish a symmetrical effect that would be most pleasing

Your fireplace appears flush or almost flush with the wall. If you build cabinets or shelves they will project beyond the fireplace and the fireplace will be recessed.

Actually the brick hearth around the fireplace extends about 4 inches from the wall - we plan on building the shelves/cabinets into the wall - so they will extend a little farther than the hearth - which is pretty typical with built-ins. We also plan on getting a new mantel.

Search pictures of fireplaces with shelves/ cabinets/ built-ins to get an idea of what you like. If you find the space is too shallow (as you would have at most 8 inches of depth for the side shelves/ cabinets if the fireplace is on an exterior wall, more if you bump the shelves back into another room) you could consider moulding that would visually distract from the side beam. The side beam is what bothers you, right? Definitely think a larger mirror/ picture would look good and a chair snugged up to one or both sides of the fireplace would be inviting. I think potentially painting the brick and using larger or a single piece of some stone for the hearth might be more to your liking. I love the sconces.

Go see a local kitchen cabinetry designer. They will show you an elevation of your current fireplace wall with various styles of built in cabinetry. Your ceiling don't look very tall, so I would not go floor to ceiling with the height. The cabinets can be build around your bulk head, so it will disappear. Choose cabinetry colour and fireplace stone to compliment the other rooms in your home so there is flow and continuity - good luck.

Above photo are of the same living room before and after.

The above photo is a beautiful solution!

wow....removing that brick really made a difference. Looks great!

A number of excellent suggestions here. You don't mention the style of your home or if you're leaning a particular way, so this is a bit of a shot in the dark.

I don't mind asymmetry if there is a strong focal point and some obvious thought in the execution of the design so it looks intentional and not lopsided. The pilaster to the left doesn't bother me either; i think Id' rather try to work it into the design instead of trying to hide it, especially since there is an obvious break at the ceiling.

I'd like to see something warm to complement the brick instead of something cool like the slate, so I'd recommend some Tennessee crab orchard stone or "rainbow" Indian sandstone, which both have some red in them to complement the brick.

As for the built-ins, I wouldn't recommend anything deeper than a bookcase on each side so the fireplace won't seem too far back. I'm also recommending bumping out the chimney breast over the top of the mantel to the same depth as the brick, which will help to make the fireplace a strong focal point and break up the horizontal line across the upper wall.

There are a lot of great things you can do with that wall . . . have fun!

Wow, Tom, that looks great, too.

Tom - nice job - what I'd do to "trick" the eye into thinking it is balanced
is make the doors larger on the right than on the left - so you have two doors on each side - lots of ways to make this work. I'm more of a symmetrical designer - so I lean that way - but this is very nice as well.