I'm sure I'll be adding to this list, so check back.
Here we go:
Removing the Grime by Tiina Nunnally on her translation (this is a treasure!)
Character chart of Real Characters in Kristen Lavransdatter
Character chart of Fictional Characters in Kristen Lavransdatter
A Tour of Bjerkebæk, Undset's home in Lillihammer (be sure to select the english version of the site)
Sigrid Undset: Catholic Viking by Steven Sparrow
A Life Worth Celebrating: Kristin Lavransdatter, by Sigrid Undset from an online LDS magazine (he he)
Under Her Heart: Motherhood in Kristin Lavransdatter by Carrie Frederick Frost at FirstThings.com (beautiful!)
A fabulous set of posts written by Webster Bull at Witness2Christ (these are great!) :
Taking Back Our Sister
Catholic Culture Needs More Champions
Are Brothers Taking Back Our Sister?
Free Will, Even in a Snake Pit
Rembering Kristen Lavransdatter
Question: Are You Saved? "writes Undset, 'no Catholic would dare to say more than that he hopes for salvation.'"
Undset's essay, "Catholic Propaganda", mentioned in above article.
"The end is a stunner, and as right as rain—worth every hour it took getting to." ~ Webster Bull. Keep writing, Mr. Bull!
Sigrid Undset Crosses Russia from the Brussels Journal
Why I am Catholic: Because This Book Really is Beautiful by our good man Webster Bull, published at Patheos.com
Sigrid Undset's Time Warp from CatholicCulture.org
Her Introduction from Penguin.com
Interesting Biography from the Great Norwegians website
Reading Sigrid Undset from catholiceducation.org
Translation of Undset's "Kristin Lavransdatter" Trilogy Gets Much-Needed Face Lift from Norway.com
A tour of Jorundard