Live histograms are a function available when viewing electronic sensor-driven views...therefore they aren't available when shooting with a viewfinder on a DSLR. In order to get a live histogram on a DSLR, you have to switch to the Live View mode - from there, if your camera is equipped with one, you should be able to cycle through the Display options and bring up a histogram. Most newer DSLRs with live view seem to have a live histogram option, but I'm not sure which models in particular from each manufacturer. Note that because DSLR live view systems are generally slow and clunky and not much fun to use unless you have to, you may just end up going with viewfinder and skipping the histogram. P&S models all are full time live view, essentially; only the mirrorless interchangeable lens cameras, Sony DSLRs, or the Sony SLT models will shoot 'normally' in live view and make it worthwhile to have the live histogram up on large sensor cameras.
Sony DSLR-A580 / Sony 18-250mm / Minolta 50mm F1.7 / Sigma 30mm F1.4 / Tamron 10-24mm / Tamron 150-600mm / Tamron 90mm F2.8 macro / Minolta 300mm F4 APO
Sony A6000 / 18-55mm F3.5-5.6 / 55-210mm F4-6.3 / 10-18mm F4 / 35mm F1.8 / 16mm F2.8 / via manual adapter, lots of Pentax K mount, Konica K/AR mount, and Leica M mount manual lenses