As another idea, I don't see the need to do this all in one regex. You have an explicit list of forbidden names, I would make an array(or hash) of those names and put that in a prominent place - not embedded in a tricky regex later in the code. Below I used a hash look-up for an exact match, but the forbidden table could also a list of patterns if it was necessary to get that complicated.

There is nothing wrong with having a number of little regexes as you continue to valid the user's input. With code written like this, reading the user error messages gives a clear picture of what is and what is not allowed without having to use brain cells thinking about the regex albiet as simple as they are below.

#!/usr/bin/perl -w
use strict;

my @forbidden = qw (
                    master
                    model
                    dbccdb
                    sybsecurity
                    sybsystemdb
                    sybsystemprocs
                    tempdb
                    DBA
                    );

my %forbidden = map{lc $_ => 1}@forbidden; 
# or could just build the hash manually

while ( (print "Enter DB name: "), 
        (my $name = <STDIN>) !~ /^\s*q(uit)?\s*$/i  
      )
{
     $name =~ s/^\s+//;
     $name =~ s/\s+$//;  #also does chomp
     
     next if ($name =~ /^\s*$/); #simple re-prompt if blank line
     
     if ($name =~ / /)  
     {
         print "Error no spaces within name allowed!\n";
         next; 
     }
   
     if ( $forbidden{lc $name}  )
     {
        print "Error: $name is a reserved name!\n";
        next;
     }
     
     if ( $name =~ /\W/)  # only a-zA-Z0-9_ allowed
     {
        print "Error: illegal character in name!\n";
        next;     
     }
     
     #... perhaps more tests on the input name?
     
     print "Ok, $name is valid\n";
}
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