We have started picking a name from a hat at Christmas and buying a present for just that one person. I hesitate to call it Secret Santa, as we were all in no doubt as to who was buying for us by the time the gifts were handed out, after many hush hush conversations about sizes, preferences, stuff that was out of stock...
There's a set amount for these presents. I also do a stocking for any adults staying over on Christmas Eve - nuts, apple, orange, silver coin, chocolate coins, sugar mouse, a book and one token pressie.
For birthdays we get a present from everyone, so exchange wish lists. Very precise ones - I always appreciate a link to the online store! We all know what the approximate spend is, but it's more flexible than at Christmas.
We buy presents as couples, but everyone gets their own gift.