Venetia by Georgette Heyer - Georgette Heyer is a recent discovery for me, and though I have enjoyed everything I have read so far, 'Venetia' and 'The Convenient Marriage' are my favourites. I also love Beauvallet.
Regency post dinner entertainment: when the men join the ladies in the drawing room, coffee and tea is served. Play no more tan 2 songs at the pianoforte if asked and if asked to join the card table, make sure you can afford to before acquiescing! You do not want debts!