Here are some of the finalists for the competition to rebuild the site in 2002.
Norman Foster's "Kissing Towers." This was a big hit with the public, and a very fine and beautiful design, arguably better than what is actually being built now. But, it relegated the Memorial to a kind of inconvenient appendage.
The design group THINK submitted this proposal. It takes the opposite approach to Foster's plan. Two skeletal towers were to rise above the sites of the former twin towers. This striking design put the memorial museum high up in the towers and included spaces for public events and performing arts. The whole site would have been subsumed into a memorial that did not make much provision for redevelopment.
This is the proposal by Peter Eisenman. Like Libeskind's design, it emphasizes a balance between memorial and redevelopment in the design. One striking feature of this proposal was a pair of parks that jutted into the Hudson River in the exact size and shape of the shadows cast by the towers at 8:46 that September morning when they were hit.
This is the United Architects proposal which I must confess I was never very fond of. To me, it looks even more like a rejected set from Metropolis than what is being built now.