Excavations carried out in the Imperial Fora in the 1990s opened up massive amounts of archaeological space to the public, but the work is far from over. As this guide went to press, the great hemicycle in the upper area of Trajan's markets was still closed for restoration and transformation into the Museo dei Fori Imperiali, a multimedia museum covering the history of urban development in this area.
Over the last couple of years the date of completion has been constantly shifting; at the time of writing the expected opening was early to mid 2007. The via dei Fori Imperiali offers a good view over all of the fora, and until the reopening of the Imperial fora you'll have to make do with that. Once the fora reopen, you'll be able to get a closer look by booking a (compulsory) guided tour at the number given above.
The visitors' centre has literature about the fora, a small exhibition area with emperors' busts and bits of pottery, as well as a bookshop, a not very nice café and a public loo.