As of April 17th, there are NEW rates going into effect:
USPS - New Prices For Mailing Services April 17, 2011 Info on the 2011 USPS Shipping Rate Increases (from Stamps.com)
On April 17, 2011 the U.S. Postal Service® will implement a postage rate increase for a number of mail classes including First Class Mail® (domestic and international), Media Mail®, and Parcel Post®. This rate change is in addition to the January 2, 2011 rate change which increased prices for Priority Mail® and Express Mail®. Priority and Express rates will not increase as a result of the April rate change.
Here is a summary of the April 2011 USPS postage rate increase:
The USPS will not change rates for Priority and Express in April 2011 (these rates were changed in the January 2011 rate change).
First Class Letters will remain at $0.44 for the first ounce and one-ounce First Class Flats will remain at $0.88; each additional ounce (or half ounce for 3.5 ounce letters) will cost an extra $0.20 (previously $0.17).
Retail rates for First Class Parcels will start at $1.71 (previously $1.22). This will be the rate for the first three ounces; each additional ounce will cost 17 cents.
The USPS will introduce Single-Piece Commercial Base and Commercial Plus Prices for First Class Parcels. Commercial Base Prices are available for all Stamps.com shippers and will save $0.15 per First Class Parcel.
Postcard rates will be $0.29 (previously $.28).
Parcel Post rates will start at $5.10 (previously at $4.90).
Media Mail rates will start at $2.41 (previously at $2.38).
Prices will also increase for certain special services such as Certified Mail, Registered Mail and Signature Confirmation.
First Class Mail International rate increases have been proposed as well. Letter prices will change for group one and group two by an average of $0.06. Flat prices will change for all country groups by an average of $0.53. Package prices will change for all country groups by an average of $0.78.
In January 2011, Priority Mail retail rates increased by an average of 3.9% (3.2% for Stamps.com/Commercial Base customers).
In January 2011, Express Mail retail rates increased by an average of 5%.
In January 2011, the USPS introduced new legal-sized Flat Rate envelopes and padded
Flat Rate envelopes for both Priority Mail and Express Mail. Pricing is the same as other Flat Rate envelopes.
Why did my shipping costs change all of the sudden? 
