23845 Raoul Bott: Lectures on Morse theory, old and new.
Bull. AMS 7/2 (1982), 331-358.

M. Goresky/R. MacPherson: Stratified Morse theory.
Springer 1988, 270p. DM 148. An important advanced text.

18136 Dusa McDuff: Floer theory and low dimensional topology.
Bull. AMS 43/1 (2006), 25-42.

Knudson: ...

J. Milnor: Morse theory. Princeton UP 1963.

J. Milnor: On the Betti numbers of real varieties. 
Proc. AMS 15 (1964), 275-280.

27907 Liviu Nicolaescu: An invitation to Morse theory.
Springer 2011, 350p. Eur 60 (Ebook).

G. Rassias: Morse theory and its applications.
World Scientific 1991, 400p. 9971-50-977-6. $58.

3783 Themistocles Rassias: Foundations of global nonlinear analysis.
Teubner Leipzig 1986.

M. Schwarz: Morse homology. Birkha''user 1993, 250p. 3-7643-2904-1. SFR 68.

2805 H. Seifert/W. Threlfall: Variationsrechnung im Gro§en.
Teubner 1938.

E. Witten: Supersymmetry and Morse theory. 
J. Diff. Geom. 17 (1982), 661-692.