First-class domestic letters will remain 44 cents, and international letters will remain 98 cents, but letters to Mexico and Canada are going up to 80 cents, and the domestic postcard rate is being raised to 29 cents.
And I just bought all those Zazzle stamps at a 28-cent postcard denomination rate!
I can't parse through the USPS website to find their full info on this, but my information comes from Your Postal Blog, which I consider a pretty darn reliable source.
Update: Thanks to Eliza Ward for guiding me to the Official USPS source for this!
I am humbled. A Canadian blog reader shows me this. Thanks, Eliza!