Here's some information about using Razor with Amavis and SpamAssassin that I collected in the process of getting stuff working.
If you are using Debian there is a package for Razor. There are probably RPMs out there also. You could install things by downloading, untar'ing, and Make'ing. But Why? 
Do this as root: "apt-get install razor"
After saying yes to downloading the dependencies and installing you have to some other steps. These are much like the RazorSiteWide steps, but specialized for Amavis.
Do these things as root and substitute the right directory and user names.
- You will substitute {amavis-home} for the diretory specified in your /etc/amavis/amavisd.conf file. Here's the variable: $MYHOME = '/var/lib/amavis'
- You will substitute {user} and {group} for the user and group specificed in your /etc/amavis/amavisd.conf file.
The variables are: $daemon_user = 'amavis'; $daemon_group = 'amavis';
- "razor-admin -home={amavis-home}/.razor -create"
- "razor-admin -home={amavis-home}/.razor -discover"
- "razor-admin -home=/var/lib/amavis/.razor -register -user postmaster@yourdomain.org" # Note I have filled in the directory here as an example. Substitute yours.
- "chown {user}:{group} .razor"
- "chown amavis:amavis .razor/*" # Note I have filled in the user and group here as an example. Substitute yours.
EXPLANATION:
- IF Amavisd-new daemon runs as the user/group "amavis" and /etc/passwd has "/var/lib/amavis" as it's home directory (which you should do when using adduser)
THEN the environment variable HOME will equal "/var/lib/amavis" when Amavisd launches SpamAssassin and also when SpamAssassin then launches Razor.
- SO, since SpamAssassin is looking for its configuration/home in /var/lib/amavis/.spamassasin and Razor is looking for its home in /var/lib/amavis/.razor, everything thing is wonderful.
- To check things out do a "razor-check -d" (for debug) and look how and what it discovers.
- Edit your "/etc/mail/spamassassin/local.cf"
- Change the "use_razor2 0" line to "use_razor2 1"