  We use the functional integral approach to study low energy collective
excitations in a continuum model of neutral two-band superfluids at T=0 for all
couplings with a separable pairing interaction. In the long wavelength and low
frequency limit, we recover Leggett's analytical results in weak coupling (BCS)
for s-wave pairing, and further obtain analytical results in strong coupling
(BEC) for both two and three dimensional systems. We also analyse numerically
the behavior of the out-of-phase {\it exciton} (finite frequency) mode and the
in-phase {\it phonon} (Goldstone) mode from weak to strong coupling limits,
including the crossover region. In principle, the evolution of Goldstone and
finite frequency modes from weak to strong coupling may be accessible
experimentally in the superfluid phase of neutral Fermi atomic gases, and could
serve as a test of the validity of the theoretical analysis and approximations
proposed here.
