Note: Parents have differing filters through which we view suitability of literature. I've grouped books based on my personal full or partial reading, YMMV (your mileage may vary).
Reader lists for concepts that may seem advanced, such as probability, often include books accessible to younger children.
The older the age level recommended, the more possibility there could be content less acceptable to your personal values. Previewing literature before handing to your children for unsupervised reading is of course recommended if you have concerns. Some are better quality than others, but all have value in my opinion. Some have beautiful artwork that increase the visual value.
Math literature is not limited to computational content. Logic, problem solving and abstract content occurs throughout literature without appearing overtly math related, but this is invaluable for developing mathematical thinking. See also related articles.
Early and Elementary Concepts
Early Concepts: Counting, Matching, Sorting, Patterns, Relationships
I Love Math and Young Math - Multi-Concept Series
Addition, Subtraction, Building Equations, Groups / Tallies
Multiplication, Skip Counting, Squaring, Division
Fractions, Decimals and Percents; Proportions and Ratios
Comparing Relative Sizes / Attributes, Estimating
Place Value and Number Bases,Groups of Ten and Hundreds
Number Properties: Pairs, Dozens, Odd & Even, Natural Groups, Zero, Negative Numbers
Upper Elem / Middle and topical
Geometry and Spatial Concepts
Measurement of Quantities and Distance, Mapping and Building Concepts
Large Numbers, Exponents, Infinity, Nested Values
Probability, Combinations, Factorials; Graphs and Data
Logic, Series, Problem Solving and Mathematical Relationships
Multi-Concept Books and Series
Language Meets Math: Poetry and Riddles, Stories and Fables with Math Ideas
topical - all ages and HS/Adult
Cultural Math, Foreign Language Counting, Math History
Math Fiction - All ages
Math in Science, Technology, Sports and Applied Math
Math in Art, Music, Nature
Time and Calendars
Biographies of Mathematicians and Scientists
Algebra, PreCalculus and Calculus
High School and Adult Math