Try to find assignments that are both interesting and fun. Games work well for this, even if they are simple. If possible, make it so students can compete with each other. Better yet, let the student's programs compete with each other.
in reply to Perl Assignments Needed
Another approach could have students create things that are useful to them. Assignments that are useful for other classes or at home would (hopefully) allow students to see the value of using Perl. This is probably harder to create and only reasonable if you see something appropriate.