  Standard model gauge bosons propagating in two universal extra dimensions
give rise to heavy spin-1 and spin-0 particles. The lightest of these, carrying
Kaluza-Klein numbers (1,0), may be produced only in pairs at colliders, whereas
the (1,1) modes, which are heavier by a factor of \sqrt{2}, may be singly
produced. We show that the cascade decays of (1,1) particles generate a series
of closely-spaced narrow resonances in the t\bar{t} invariant mass
distribution. At the Tevatron, s-channel production of (1,1) gluons and
electroweak bosons will be sensitive to t\bar{t} resonances up to masses in the
0.5 - 0.7 TeV range. Searches at the LHC for resonances originating from
several higher-level modes will further test the existence of two universal
extra dimensions.
