W. Hackbusch: Integral equations, Birkhaeuser Verlag, 1995.
(Textbook on integral equations treating both theoretical  and numerical aspects, Chap. 1, 3.5, 4.3-4.5, 8, 9)

W. McLean: Strongly elliptic systems and boundary integral equations,  Cambridge, University Press, 2000.
(Theory of boundary integral equations  and prerequisites in functional analysis. Chap 3, and possibly 6,7)

R. Dautray and J.-L. Lions: Mathematical Analysis and Numerical Methods for Science and Technology. Vol. 4, Chap. XI, pp. 114-159.
(Introduction to boundary integral equations and Galerkin boundary element methods)

M. Bonnet: Boundary Integral Equation Methods for Solids and Fluids. Wiley, 1995.
(Includes are broad range of application areas)

G. Chen and J. Zhou: Boundary Element Methods. Academic Press, 1992.
(Covers most areas of boundary integral equations and classical discretization methods)

K. Atkinson: The numerical solution of integral equations of the second kind. Cambridge, University Press, 1997.
(Focus on integral equations of the 2nd kind and collocation methods)

M. Costabel: Boundary integral operators on Lipschitz domains. Elementary results. SIAM, J. Math. Anal.19, pp. 613-626, 1988.
(Original paper containing the mapping properties of classical integral operators and regularity results.)

T.v. Petersdorff, C. Schwab: Fully Discrete Multiscale Galerkin BEM. Download: ap.ps.gz

S. Sauter: Variable order Panel Clustering. Download: Abstract / Preprint

S. Erichsen und S. Sauter: Efficient automatic quadrature in 3-d Galerkin BEM . Download: arbkern.ps

W. Hackbusch: A Sparse Matrix Arithmetic Based on H-Matrices. Part I: Introduction to H-Matrices. Erschienen in: Computing Vol 62 (1999), 89-108.