FlexDen providing sample applications for the flex developers. They have many interesting application in their website. Here is the some of the applications from that. You can download source codes of these applications also if you like. i have given links to some applications, you can find more applications by searching in website.

Free Flash Catalyst Flex 4 Custom Buttons
http://www.flexden.net/content/free-flash-catalyst-flex-4-custom-buttons

Free Flex Black Gloss Skin
http://www.flexden.net/content/flex-black-gloss-skin

Free Flex RSS Reader
http://www.flexden.net/content/flex-rss-feed-reader

Free Custom Flex Sliders
http://www.flexden.net/content/custom-flex-sliders

Free Flex Twitter Pod component
http://www.flexden.net/content/flex-twitter-pod-component

Free Flex Category XML Video Player
http://www.flexden.net/content/flex-category-xml-video-player

Free Flex Horse Preloader
http://www.flexden.net/content/flex-horse-preloader

Free Flex Water Image
http://www.flexden.net/content/flex-water-image

Free Flex Company Preloader
http://www.flexden.net/content/flex-company-preloader

Free Flex XML news Application
http://www.flexden.net/content/flex-xml-news-application