Well, I always fill areas like that with bookcases, but that's not for everyone. How about a console table? Or a skinny storage unit of some kind (most folks can use more storage). I think the space is too small for a dining table.

As to the rest, I think I'd be more inclined to have a coffee table rather than an end table (you don't have a lot of room to get around that sofa but there's plenty of room for a coffee table). You might think about getting an occasional chair in there to make for a conversational grouping around the fireplace and sofa, although, again, the space looks a bit tight.

I'd put a console table and ottomans behind the sofa, like this:

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