Things I'd love to read about if I had more time are: topology (knots are weird interesting things), meta-mathematics (Gödelization and all that, read Gödel, Escher, Bach if you'd like to wet your appetite), paraconsistent logic (how to contain inconsitencies in systems of logic so that they don't become arbitrary - as from contradiction, anything follows). Digesting maths requires a _lot_ of time, wish I could be a student again to sit in whatever lecture that sounds interesting.
As a kid, I loved reading about history of maths; many discovery stories made me become a scientist (applied computer science researcher), and I still enjoy reading about it (also biographies or even mathematically related fiction e.g. The Solitude of Prime Numbers).