Unlike the other cities nearby, Arles isn't just a one-attraction deal as in addition to the Roman ruins that are commonplace in the area, they also have Vincent Van Gogh.
That duality is reflected in the tourist promotions and everywhere you'll find that the Roman history and Van Gogh get equal billing. Thrown into the mix is also the Camargue, a large nature reserve.
The town itself is quite small and you could easily see all of the major attractions in a day without rushing.
Of the Roman remains, the major ones are the theatre, the amphitheatre (usually called the "arene"), the thermal baths and the Alyscamps (a necropolis). All are quite well preserved. The entrance charge is around EUR 5 but you can buy combination tickets which cover several of the Roman sites and usually a few museums too. As you would expect with such a rich Roman heritage, the town has a considerable number of museums to display it all.
The Church of St Trophime has what is considered to be one of the finest examples of romanesque sculpture in its depiction of the Last Judgement over the entrance.
Van Gogh represents the second major strand of attractions. Although none of his works are on display in the town you can walk around the various sites of his paintings and can have a meal in the cafe (to get the view as he saw it, eat in the cafe just beside it).
Finally, the Camargue is right on the doorstep of the town. This park is home to over 400 species of birds and, unfortunately, a considerable number of mosquitos. It's perhaps most famous for the Camargue horses and bulls.
The nearest airport is Nimes (FNI) but Avignon (AVG), Nice (NCE) and Montpellier (MPL) aren't far so you've an excellent choice of flights from discount and major airlines.
The town is easily reached by train. You can get the TGV to Avignon which can also be reached by Eurostar from London during the Summer (change at Lille at other times).
