Spectrums or spectra are both accepted plurals of spectrum.
Statuses and status are both accepted plurals of status. Status is the more common of the two.
Both strata and stratums are accepted plurals of the Latin noun, stratum.
Swine is used for both the singular and plural forms of swine (as in the ruminant, the pig).
Symposium comes from Latin, and so its original Latin plural form is symposia. Over time and frequent misuse, symposiums has also become accepted as a plural.
Both antennas and antennae are plurals for antenna. The original Latin plural is antennae.
Beaus and beaux are both accepted plurals for beau.
The plural of bureau, which comes from the French, is bureax or bureaus.
Chateau, which comes from the French, accepts chateaux and chateaus as a plural noun.
Formulas and formulae are both accepted plurals of formula.