Good Fortran Compiler for computational science on PC?

 Hi Computational Chemists:
      This is a computer-related question but also a little computational
 science-related.
      We are developing some quantum calculation codes.  According to our
 test, the performance of Intel Pentium-100 is around 1/2-1/5 of an
 IBM/RS6000 3CT (the same CPU as 590).  And, surely, Pentium is much much
 cheaper.  According the last issue of Byte magzine, the PentiumPro-200
 (P6), with SPECint92=~360, SPECFp92=~260), is as fast as IBM/RS6000 3CT.
 But the problem comes, we don't any good Fortran90 compiler.  We just
 tried Microsoft Fortran PowerStation 4.0.  It has very nice developer
 interface and is quite easy to use.  However, it only compiles small test
 programs; for big 'real' programs, we just got a lot of ridiculous errors.
 Afer two weeks work, we returned it.
     So, we want to know is there any computation chemist using PC as a
 calculational power and can anyone suggest a good Fortran 90 compiler?
     If there is any good Fortran90 compiler, it seems to us that PC can
 be a much cheaper choice for scientists.
     Thanks in advance.
 Taisung Lee