Over the course of three decades from the late 1930s on Charles W. Cushman of Indiana traveled the world and photographed what he saw on colour Kodak slides. On his death some 14,500 of these were bequeathed to Indiana University, who have made the collection available online.
By any standards this is an amazing body of work: for colour and quality they already stand out from most photography of that era, but throw in the range of locations and subjects, and Cushman’s eye for composition and interesting detail and there’s a lot of wonderful stuff here.
Cushman went all over: there are thousands of photos from the US, and hundreds from the UK. Best of all, there are a few dozen from Ireland, including some fantastic shots from a June 1961 visit to Dublin.
[edit: Forgot to say, you can get a much bigger version of each photo by clicking the links provided]
Here is College Green, not much changed apart from the traffic:

O’Connell Bridge and the Liffey:

On O’Connell Bridge (complete with flags, green bus and Bolands delivery van):

On O’Connell St itself (they didn’t seem to go in for road markings much in those days):

Cyclists at the bottom of Great Georges St:

And further up Georges St (the Long Hall hasn’t changed much!):

And lastly for Ireland, here’s one from the Vico Road looking over Killiney Beach and up to the hill, so bright and clear it could have been taken yesterday:

Then there’s London, also in the early 1960s. There are great shots here of Trafalgar Square, Picadilly Circus at night, a ‘huckster’ in Aldgate market, a couple of authentic urchins, the Hippodrome when it wasn’t such a dive, and Covent Garden when it was still a working market (with old-school market men who could balance stacks of pallets on their heads). I love this shot of the South bank of the Thames east of London Bridge, when an area that is now a mix of offices (featuring insufferable yuppies like me) and various cultural activities was solid working docks.

Some of the best stuff comes from the Moorgate area. I’m including this one because I’ve actually been up in that tower (Pat works in the offices below):

And then there’s this one, probably the shot of the collection for me, looking north from London Wall over land still lying waste after the devastating bombs of WWII to the church of St Giles-Without-Cripplegate:

Five years later Cushman returned to find them building the Barbican around St Giles:

The earliest photos are American, and the effect of seeing things from such an early age in such vivid colour is pretty jarring. Here is a New York City street scene from 1941:

Here’s a hot-dog stand and here’s McSorley’s Old Ale House on East 7th St, which is still there today, more than can be said for many of the lower Manhattan neighbourhoods Cushman photographed.
Finally, proof that times really have changed: in 1941 even the bums were well-dressed:
