Brynjolf's sales pitch for Genuine Falmer Blood Elixir always makes me smile. I tend to put off doing the thieves guild quest for as long as I can (or I never do it), just so I can hear it whenever I'm shopping.
Being from the north of England (and married to a Londoner), I can imitate his Scottish accent well enough to amuse my spouse at least. Though I'm not sure what the clerk at the pharmacy thought when I blurted out: "Live for thousands of years, see into other people's thoughts, grrrow back that missing limb!"