beach in Italy between Venice and Rome ??

I suggest you get the beach out of your system by going to Vieques or Culebra for a week before going to Italy. Or at least go to the Playa de Luquillo. You won't find anything much better than the Condado beach anywhere near Rome or Venice. The closest beaches to Rome are at Ostia Lido and Fiumicino (both no better than Condado). Fregene and Santa Marinella, north of Fiumicino airport are a bit better. Near Venice there is the Venezia Lido. Not a big deal. The Lido di Jesolo, a little north, is better (my cousin used to go there when we were kids, she liked it). There are some nicer beaches elsewhere but nothing close to where you go. The best beaches (truly gorgeous) are of course in Sardinia and also in the Tuscan Archipelago. But that's even harder to get to than Capri (which has no beach, just cliffs). Also eat plenty of arroz con gandules, tostones, maduros and mofongo before you go, because you'll be stuck to eat pasta for a while and you might miss your "comida boriqua".

Check out the Ron in Rome website for information on Lake Bracciano which is reachable by train from Rome. There are some beaches along the coast near Rome - Ostia Lido for example, again easily reached by train from Rome. From Venice it should be possible to visit Rimini a big resort town in Umbria... And of course there is the Venice Lido - a vaporetto ride away from Venice. All depends on what you are looking for - sun, sand and sea, then Ostia, Rimini and the Lido will fill the bill. If you want scenery as well, then the lake might be better.

The Romagna coast is flat with big beaches, similar to Florida (Miami, Ft.Lauderdale) in some respects. Rimini is in Romagna, not Umbria. Umbria is landlocked, no beaches there.

If you're going to be in Italy in mid-August, be advised that half of the country will already be at the beaches. The other half will be up in the mountains.