Spivak · Calculus
The rigorous calculus textbook. Real-analysis-flavored, problems that teach.
★★★★★ · 540 problems · UG analysis
Apostol · Calculus I & II
Integration-first treatment, classical exposition. Vector calculus included.
★★★★★ · 720 problems · UG
Rudin · Principles of analysis
"Baby Rudin." The benchmark for real analysis at the undergrad/grad bridge.
★★★★★ · 380 problems · UG–grad
Strang · Linear algebra
MIT's flagship LA textbook. Geometric, computational, accessible.
★★★★★ · 520 problems · UG
Putnam archive
75+ years of the hardest undergrad math competition in the US.
★★★★★ · 900+ problems · UG-elite
IMO archive
All problems from every International Mathematical Olympiad since 1959.
★★★★★ · 360 problems · pre-college elite
Hatcher · Algebraic topology
The free standard text. Hard, beautiful, the road into topology.
★★★★☆ · 240 problems · grad
Dummit & Foote · Abstract algebra
Comprehensive grad text. Groups, rings, fields, Galois theory, modules.
★★★★★ · 600 problems · grad