H. Croft/K. Falconer/R. Guy: Unsolved problems in geometry.
Springer 1991, 200p. 3-540-97506-3. DM 87.

G. Gilbert/M. Krusemeyer/L. Larson: The Wohascum county problem book.
AMS 1993, 230p. $26. 130 interesting problems for undergraduates with
complete solutions.

24135 Timothy Gowers: Rough structure and classification.
Geom. Funct. Analysis, Special Volume (2000), 39p.
A collection of open problems in contemporary mathematics.

P. Halmos: Problems for mathmaticians young and old.
Mathematical Ass. of America 1991, 320p.

Klee/Wagon: Old and new unsolved problems in plane geometry and number theory. 
Mathematical Ass. of America 1991, 330p.

17036 Paulo Ney de Souza/Jorge-Nuno Silva: Berkeley problems in mathematics.
Springer 2004, 590p. $45.

22860 Stephen Smale: Mathematical problems for the next century. Internet 1998, 29p.