  Magnetically-tunable Feshbach resonances are an indispensable tool for
experiments with atomic quantum gases. We report on twenty thus far unpublished
Feshbach resonances and twenty one further probable Feshbach resonances in spin
mixtures of ultracold fermionic 40 K with temperatures well below 100 nK. In
particular, we locate a broad resonance at B=389.6 G with a magnetic width of
26.4 G. Here 1 G=10^-4 T. Furthermore, by exciting low-energy spin waves, we
demonstrate a novel means to precisely determine the zero crossing of the
scattering length for this broad Feshbach resonance. Our findings allow for
further tunability in experiments with ultracold 40 K quantum gases.
