Well, Jered, theres .SMD, .MD2, .MD3, .BOt, .MESH, .LWO, .3DS, . ASCII...
Theres an infinite (or close to it) number of model types. However, 3DGS can only use .MDL and .HMP. The signle best tool for conversion is Milkshape 3d, though you can often find pulgins to convert from one program to a more popular one then improt to med (i.e. a program that used .MESH will export to .3DS which MED can import)
... .MDX, .TMD, .NIF, .SKA, .X, .RIB, .DFX, .INC...