Frank II: I second the advice to post at Flyertalk. However, I can tell you now that I don't believe there are any daytime flights from the US to cities other than London (which makes me sad, as I am a fan of these too.)
The main reason is that these daytime flights generally leave quite early in the morning in the US or arrive fairly late at night in London. This means that it is difficult for anyone who needs to make a connection, either from another US city or to another European city. Taking some of the flights mentioned earlier, if you arrive at LHR at 9 pm, it's basically too late to make a connection to anywhere else in Europe; if you're leaving EWR at 8:30 am, you'd have to get up impossibly early to make a connection from somewhere else in the US (Cincinnati is roughly a 2-hour flight: to make an 8:30 am departure from EWR you'd need a Cincinnati-NYC flight departing sometime around 5:30 am at the latest, which would not be very popular.)
So this means that from an economic perspective these daytime flights basically have to rely on a sufficient number of "O&D passengers," or "origin & destination passengers" -- passengers who are not making any connections on either end. London is basically the only market strong enough to support these kinds of flights, and you'll notice they are from major US markets only - NY, Boston, Chicago, DC, Toronto.
In addition, as mentioned, London is 6 hours ahead of the East Coast while almost all of continental Western Europe is 7 hours ahead. Given that many European airports have curfews (Frankfurt bans landings after 11 pm), it makes very late arrivals, and late connections from London infeasible. There are also economic reasons about the usage of aircraft, and finally a lot of people don't like taking these daytime flights because they feel they are "wasting" a day.