I'd never heard of them before this book landed on my doorstep, but I'm kind of in love with Arne & Carlos, the Norwegian duo behind 55 Christmas Balls to Knit, a book devoted to spherical holiday ornaments with a traditional Scandinavian flair.
The book is a little glimpse into their studio (which is also their home, in an old train depot up in the mountains of Norway), their inspiration and their love of Christmas and wintertime. This book is worth a look just to see their amazing inspiration books, which clearly illustrate where the ideas for different motifs came from.
And there are a wide range of motifs, from religious-themed ornaments to hearts, reindeer, Christmas trees, skiers, sledders, even a witch (you'll have to read the book for the story behind that one).
All the balls use the same basic pattern, so you can easily add any motif you like or knit a plain ball using a different kind of yarn for a completely different look.
These small projects are fast and easy if you know how to increase, decrease, read a chart and do stranded colorwork. You could easily knit up a bunch to decorate a special tree, use on your presents or give as gifts to people who come to Christmas dinner at your house.