CL-INTERPOL is a library for Common Lisp which modifies the reader so that you can have interpolation within strings, similar to Perl or Unix Shell scripts. It also provides various ways to insert arbitrary characters into literal strings even if your editor/IDE doesn't support them.
CL-PPCRE is a portable regular expression library for Common Lisp. It is compatible with Perl, and it's fast, portable (strictly ANSI-compliant), and thread-safe. It comes with convenient features like a SPLIT function, a couple of DO-like loop constructs, and a regex-based APROPOS feature similar to the one found in Emacs. In addition to specifying regular expressions as strings like in Perl, you can also use S-expressions which are more Lisp-y.