Funny I was just thinking about this!
I felt like I had a significant clearing of brain fog when I began supplementing some amino acids that I was low in (serine, glycine, lysine). The improvement was fairly dramatic at the time, I felt like I went from around 20% cognitive function to closer to 50%. Specifically I felt like my working memory improved, so I was better able to follow spoken conversations and read. Previously I had trouble because by the time I got to the end of a sentence I would have forgotten the beginning! I still have trouble with this when I've pushed myself too much.
And unfortunately, 50% still ain't that great
One other thing which I find oddly helpful is an audio app I have on my iPhone that is supposed to effect your brainwave (I know it sounds hokey!). I have gone back to work (it was either that or LTD and I wasn't ready for the later) recently, and I have found that listening to this (with my headphones) helps me focus much better. I still feel like my brain is slow and mushy, but I am better able to start and stick with a task. My husband (healthy) also has the program but uses it for power naps, and swears by it.
The app is called "AmbiSci Entrainment Effects" and there are different bundles with different options (sleep, meditation, etc.), the 'entrainment' I use is "Focus". There's also another one called "Brainwave", but I haven't used this one as much and so am not sure how well it works for me. I suspect these, or something similar, are available in other formats if you don't have an iphone (android, use on your computer or downloading as an mp3?).
That's only two, but that's all I've got. Looking forward to other's responses and ideas!