Higher-Order Perl: Transforming Programs with Programs - Probably old news to most Perl folks but MJD has been writing this book for quite some time. While it’s been developing on his site (and you’ll still be able to get it there), it’s great to have a physical book. (Plus it’s good to shove some money toward smart people doing good work.) Lots of CS-meets-Perl type material, especially regarding functional programming.