We study concentrated binary colloidal suspensions, a model system which has a glass transition as the volume fraction $\phi$ of particles is increased. We use confocal microscopy to directly observe particle motion within dense samples with $\phi$ ranging from 0.4 to 0.7. Our binary mixtures have a particle diameter ratio d_S/d_L=1/1.3 and particle number ratio N_S/N_L=1.56, which are chosen to inhibit crystallization and enable long-time observations. Near the glass transition we find that particle dynamics are heterogeneous in both space and time. The most mobile particles occur in spatially localized groups. The length scales characterizing these mobile regions grow slightly as the glass transition is approached, with the largest length scales seen being ~ 3 small particle diameters. The glass transition occurs at phi_g \approx 0.58, with characteristic signs of aging observed for all samples with phi>phi_g.