Until today (June 3, 2016), Starwood Preferred Guest personal or business credit cardholders can buy up to 30,000 Starpoints with up to a 35% discount on the normal purchase price.

You can earn 10,000 Starpoints per referral to the Starwood Preferred Guest Credit Card, up to 55,000 Starpoints per calendar year. That's double the normal Starpoints per referral (but the same annual cap.)

I value 10,000 Starpoints at $250 and 55,000 Starpoints at $1,375.
How does the referral bonus work?
Look for an email with the subject "Limited Time: Refer a Friend, Earn Double the Starpoints" and click the Refer Now button.

Until today (April 30, 2016), you can buy up to 30,000 Starpoints with up to a 25% discount on the normal purchase price.

Starpoints are normally sold in increments of 500 points for 3.5 cents per point.

Effective immediately, you can transfer SPG Starpoints to Virgin Elevate points at a 1:1 rate. Like all 1:1 partners of SPG, you get 5,000 bonus miles for every 20,000 points transferred, so 20,000 Starpoints equals 25,000 Virgin America points. This is 2-and-a-half times the Virgin America points that you get from competing transferable points.

The Starwood Preferred Guest personal and business credit cards from American Express now come with 35,000 bonus Starpoints for spending $3,000 and $5,000 respectively in the first three months of cardmembership.

Links:

Starwood Preferred Guest® Credit Card from American Express (personal)
Starwood Preferred Guest® Business Credit Card from American Express

The normal sign up bonus is 25,000 points, the twice yearly limited time offer is 30,000 points. This is the highest public sign up bonus ever on these cards.

The Chinese insurance company Anbang has topped Marriott's latest bid for Starwood, the company that manages these hotel brands.

This soap opera has been ongoing since November when Marriott offered $72.08 per share for Starwood. Anbang and Marriott have gone back and forth with the latest Anbang offer worth $82.75 per share.

I haven't been covering the twists and turns and won't cover them again until a sale is completed.

Aeroplan has brought back its huge transfer bonuses that it last offered in April, August, and December 2015.

Right now 40k Starpoints plus taxes will get you a roundtrip economy class trip to Europe, 145k Starpoints will get you two roundtrip Business Class ticket to Europe, and 110k will get you two roundtrip First Class tickets to Hawaii.

Starpoints always transfer to dozens of airlines at a 1:1 rate with a bonus of 5,000 miles for every 20,000 Starpoints transferred.

Update 8/30/15: This offer ends Monday August 31, 2015.

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Until August 31, 2015, you can transfer 20,000 SPG Starpoints to 30,000 American Airlines AAdvantage miles.