Recently Read Pop-Sci (Math)

'Mathematics: A very short introduction' by Timothy Gowers
'Letters to a young mathematician' by Ian Stewart
'A mathematician's apology' by G.H. Hardy with foreword by J.P. Snow (brilliant!)
Currently reading the 'further reading' sections of these books.

Also reading 'The Ph.D. Process: A student's guide to Graduate school in the sciences'. Heavily lab-science based but still has some interesting and noteworthy ideas. Everyone should read this before they graduate if they're even considering a postgraduate degree in the sciences.