Site59 and Travelocity feature the same packages, and yes they can provide a savings of many hundreds of dollars on airfare alone.

I've used Site59 a couple of times for weekend trips to London. One of these was in mid-July from JFK to LHR, a month and route when even the lowest fares routinely run over $800 roundtrip. Site59 offered an "Air and More" package, with a nonstop on AA in both directions and a dinner at the Hard Rock Cafe, for less than $500. And in September, I paid $435 for another JFK-LHR AA roundtrip--- including one night's stay at a Holiday Inn in central London. I added a cheap Independence Air flight from IAD to JFK (just over $100 r/t, booked separately) and had myself a blast.

Unfortunately, most of the Site59/Travelocity packages are only valid for Thurs/Fri/Sat travel on the outbound and a Sun/Mon/Tue return, so for business trips they don't usually fit unless you want to spend a few extra days at your destination.