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A Wrangler's shortlist
Complex Algebraic Curves (London Mathematical Society Student Texts)Complex Algebraic Curves (London Mathematical Society Student Texts) by Frances Kirwan
Buy new: £28.49 / Used from: £25.18
Covers around half of the 3rd year Riemann surfaces course. Lots of nice illustrations of algebraic curves.
Linear Analysis (Cambridge Mathematical Textbooks)Linear Analysis (Cambridge Mathematical Textbooks) by Bila Bollobás
Buy used from: £9.92
Covers all of the 3rd year Linear Analysis course. Some very hard exercises.
REAL & COMPLEX ANALYSIS 3E (5P: Mathematics Series (McGraw-Hill International Editions: Mathematics Series)REAL & COMPLEX ANALYSIS 3E (5P: Mathematics Series (McGraw-Hill International Editions: Mathematics Series) by Walter Rudin
Buy new: £32.78 / Used from: £25.00
Useful for 3rd year Riemann surfaces and Linear (Functional) Analysis
Problems in Algebraic Number Theory (Graduate Texts in Mathematics)Problems in Algebraic Number Theory (Graduate Texts in Mathematics) by M. Ram Murty
Buy new: £43.69 / Used from: £15.52
Good for Number Fields and the Number Theory C course.
Probability with Martingales (Cambridge Mathematical Textbooks)Probability with Martingales (Cambridge Mathematical Textbooks) by David Williams
Buy new: £23.08 / Used from: £20.00
Probabilistic approach to Probability and Measure. Martingales are the correct approach to many of the theorems in the course.
Algebraic TopologyAlgebraic Topology by Allen Hatcher
Buy new: £17.88 / Used from: £16.75
'Nuff said
Algebraic Geometry (Graduate Texts in Mathematics)Algebraic Geometry (Graduate Texts in Mathematics) by Robin Hartshorne
Buy new: £45.37 / Used from: £27.00
The bible for algebraic geometry. Soon to be an undergraduate course.
A Course in Galois TheoryA Course in Galois Theory by D. J. H. Garling
Buy new: £20.99 / Used from: £8.08
Far greater coverage than Stewart though more difficult to read.
General Relativity: An Introduction for PhysicistsGeneral Relativity: An Introduction for Physicists by M. P. Hobson
Buy new: £33.80 / Used from: £33.41
Much more easy going than most general relativity books and with similar content in terms of differential geometry.
A Classical Introduction to Modern Number Theory: v. 84 (Graduate Texts in Mathematics)A Classical Introduction to Modern Number Theory: v. 84 (Graduate Texts in Mathematics) by Kenneth Ireland
Buy new: £43.99 / Used from: £30.71
Excellent coverage of 3rd year number theory.
Linear Representations of Finite Groups: v. 42 (Graduate Texts in Mathematics)Linear Representations of Finite Groups: v. 42 (Graduate Texts in Mathematics) by Jean-Pierre Serre
Buy used from: £25.64
Most likely the best choice for Representation theory. Fulton and Harris is a little advanced for undergrad's.
Quantum PhysicsQuantum Physics by Stephen Gasiorowicz
Buy new: £39.79 / Used from: £38.50
Nice easy going book with plenty of illustrative examples that really makes Quantum Mechanics easy. Not written for mathematicians but has the content.
Partial Differential Equations (Graduate Studies in Mathematics)Partial Differential Equations (Graduate Studies in Mathematics) by Lawrence C. Evans
Buy new: £56.00 / Used from: £45.00
Decent book for PDEs. See also Rudin's Real and Complex Analysis.
A Hilbert Space Problem Book (Graduate Texts in Mathematics)A Hilbert Space Problem Book (Graduate Texts in Mathematics) by P.R. Halmos
Buy new: £41.79 / Used from: £33.07
Complements Linear Analysis and Hilbert Spaces (now defunct) courses
Probability and Random ProcessesProbability and Random Processes by Geoffrey Grimmett
Buy new: £30.03 / Used from: £29.00
A good choice for Applied probability
Options, Futures and Other DerivativesOptions, Futures and Other Derivatives by John C. Hull
Buy used from: £35.00
Default book for Stochastic financial models. Solutions book also available.