i would go with the s2000...
120hp/l
and i don't care what people say about the lack of tq. get in one and stomp it and see if the 9k's of rev through each gear is enough for ya..
i like some of your other choices.. like the is300 but it's the same price as the s2k.. and a used s4 would be sweet.. i would quite enjoy one of those..
some of the cars on the list have the s2k beaten in power or some in luxury and so on and so forth but i think the s2k is the best for the money.. 32k... and it is limited production.. this was supposed to be the last year but they are making the 2003, so wait just a bit and get a brand new 2003, although there are no changes from 2002 to 2003...
but it also depends on what your drivin it for..
the evo and the wrx, are rally cars.. and the is300, and the s4 or a4 are luxury, and the s2k is a sunday racer and a daily driver.. so it all boils down to what you need it for..