you can use the Merge Edge Tool which is in Edit Mesh - or you can hold down Shift key and RMB (right mouse button) and it's the first option up.
then you'll see the 'boundaries' of where the gaps are (ie. where the faces are not continuous) highlighted in solid/thick blue line. you just double click on the edges one by one and your faces will be merged together.
However before you can do that, you'll have to combine all the seperate geometries/faces together...which is in Shift+RMB, Combine. or Mesh > Combine.
hope that helps.
-f
oh yeah, also if you dont want to double click a few hundred times on those bold edges, you can just select all the vertices after the surfaces have been combined and just hit Shift+RMB > Merge Vertices > Merge Vertices.
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