Am not participating regulartly on giveaway contests. I only participate if I think the product is useful for me. I won the following giveaways, and from day I won (I received the license exactly) am using these things.
1. TechPP Mega Christmas Giveaway SnagIt 9.1 Giveaway (28th November 2009) -
Conducted from 25th November 2009 to 26th Nov 2009. And am still using this for my screen capturing needs. Thanks to Raju PP 
2. Windows Lifestyle Windows 7 home premium and Microsoft Office 2010 Professional Plus (15th July 2011) -
Am using the Windows 7 home premium on my second PC ( Ultimate on the other one) and still using the Microsoft Office 2010 Professional Plus for my primary use. Thanks Nitin Agarwal
3. Tamil @ My Opera- Tamil New Year Giveaway: Introducing HTML5 Book. (24th May 2011)
This is a really cool book, and I have covered half of it. This is Signed copy. Actually am soo lucky to get this book because first three winners of the book did not claim this and I was the fourth one. Thanks Tamil. Also thanks Aleksander for Sending the book to Tamil.
4. DotNetCurry - Telerik JustCode Add-in For Visual Studio (3rd June 2011)
I must say that this is a real cool add-on for Microsoft Visual studio, which will reduce your efforts and chances for errors. When ever I came to know I won I downloaded and installed a trial version of JustCode, and it was really handy.
Thanks Suprotim Agarwal and Carol.