So many. Without stating the obvious, the whole Vivian Maier story amazes me and makes her photography all the more intriguing.
I had the pleasure of meeting Ulla Lohmann at the UK Photography Show this year, she was wonderful and her work has wowed me ever since. She lowers herself into active volcanoes and takes the most awe-inspiring photos: https://www.instagram.com/ullalohmann/
I love looking at photojournalism, so most photojournalists inspire me too (namely Steve McCurry).
As a total aside though, my recent find on Instagram is Henry the Colorado Dog... love this feed.