Rightclick -> Select All [Something]
If you want everything except StaticMeshes rightclick a StaticMesh, chose Select All StaticMeshes open their properties and change the Object Group name to something. Now open the Groups browser, click Refresh, "deselect" the group and uncheck the box to hide it in the editor. Now go back, draw a rectangle around the whole map (ctrl+alt+ drag left mouse) to select everything (except the StaticMeshes you just hid).