I think that the title is self-explanatory but I'm thinking about mathematical subjects that have not received a full treatment in book form or if they have, they could benefit from a different approach. (I do hope this is not inappropriate for MO).
Let me start with some books I would like to read (again with self-explanatory titles)
1) The Weil conjectures for dummies
2) 2-categories for the working mathematician
3) Representations of groups: Linear and permutation representations made side by side
4) The Burnside ring
5) A functor of points approach to algebraic geometry
6) Profinite groups: An approach through examples
Any other suggestions ?