TOMS379 is a FORTRAN77 library which implements ACM TOMS algorithm 379, for estimating the integral of a function over a finite interval.
The text of many ACM TOMS algorithms is available online through ACM: http://www.acm.org/pubs/calgo or NETLIB: http://www.netlib.org/toms/index.html.
TOMS379 is available in a FORTRAN77 version.
INTLIB, a FORTRAN90 library which includes many routines for estimating the integral of a function.
QUADPACK, a FORTRAN90 library which includes many routines for estimating the integral of a function, including weight functions, singularities, and infinite intervals.
QUADRULE, a FORTRAN90 library which defines many simple quadrature schemes.
STROUD, a FORTRAN90 library which defines quadrature schemes for a number of geometrically interesting regions.
TEST_INT, a FORTRAN90 library which contains routines which define integrands suitable for testing integration software.
TOMS351, a FORTRAN77 library which carries out Romberg integration of a function.
TOMS468, a FORTRAN77 library which carries out automatic integration of a function.
You can go up one level to the FORTRAN77 source codes.