For boxed ones, I really enjoy the Peak Freans (or however you spell it) digestives with chocolate on them. I'm having some now with my tea.
For homemade I really enjoyed some simple chocolate chip cookies I made once. I got the recipe from the back to the chocolate chip bag. They were milk chocolate chips and I added shredded coconut to the dough. It made them nice and chewy.
I also like these pain d'amande cookies.
They're a wonderful combination of buttery and crispy. Mmmm. Plus the dough freezes well so I can just bake up a few at a time and they last forever!