Amazon: Kindle Is Still No. 1 Product, Now Includes 500,000 Titles just reported strong earnings for the first quarter of 2010, with net sales increasing by 46% to $7.13 billion in the first quarter, compared with $4.89 billion in first quarter 2009. Amazon says the Kindle remains its bestselling product with the number of books in available for the device reaching 500,000 titles.

Operating income increased 62% to $394 million in the first quarter, compared with $244 million in first quarter 2009. Net income increased 68% to $299 million in the first quarter, or $0.66 per diluted share, compared with net income of $177 million, or $0.41 per diluted share, in first quarter 2009.

Amazon is clearly emphasizing Kindle sales and its status as their premier product in response to the potential competitiveness from Apple’s tablet device, the iPad. Amazon subsequently released its own iPad app for the Kindle, to compete with iBooks. For the quarter, Amazon reported that worldwide electronics and other general merchandise sales grew 72% to $3.51 billion. The U.S. Kindle Store now has more than 500,000 books, which Amazon says includes 100 of 111 New York Times Bestsellers, more than 9,000 blogs, and more than 175 top U.S. and International newspapers and magazines.

Amazon also highlighted the success and international expansion of Amazon Prime, the subscription product that gives customers free two day shipping on everything they buy from Amazon. Amazon was recently reported to be launching a promotion to give all Amazon Prime customers a free Kindle.

In terms of of total sales, International sales, which include revenue from the company’s U.K., German, Japanese, French and Chinese sites, were $3.35 billion, up 45% from first quarter 2009. U.S. and Canada sales came in at $3.78 billion for the quarter, up 47% from first quarter 2009.

The e-commerce giant also recently announced that the Kindle would be available for sale at Target stores, which is the first availability of the device in a brick and mortar store. In the earnings call, Amazon CFO Tom Szkutak said the vision for the Kindle was to have every book ever published available in all languages and that’s still the aim for the future.