I use RCS as well. Simple. Works.

mkdir RCS
ci -u file.pl # check in file (inital touched version)
co -l file.pl # check out file to make revisions
....
rlog file.pl # history of a file
rcsdiff -r1.2 file.pl # diff versions of files
co -r1.2 file.pl # get an earlier version of a file
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You can also use string subistutions to display version numbers in line of the file, but I haven't gotten that to work (yet)... Like perl, it's simple and just works...
Update:
Here's code that allows you to display the Id tag, which includes version number, last modified date, who updated it, etc.:

my $v = q{$Id$};
print "$v\n";

or simply
# $Id$
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Yet Another Update:

rlog file.pl # display a log history of the file changes from version 
+to version...
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