Looks more and more like Lychnis/Silene... maybe even Silene x robotii 'Rolly's Favorite', as you've shown, Lin. It would be a good guess, as it came out a few years ago and is probably pretty common in the stores.
Edit... Nah, I take it back. The dark leaves are still saying Lychnis x arkwrightii*cv. such as 'Vesuvius' or Lychnis x haageana**.
*http://www.google.ca/search?q=lychnis+arkwrightii&client=safari&rls=en&source=lnms&tbm=isch&sa=X&ei=cMN6U4abIpC9oQTb4YH4Dg&ved=0CAgQ_AUoAQ&biw=1078&bih=990
**http://www.google.ca/search?q=lychnis+haageana&client=safari&rls=en&source=lnms&tbm=isch&sa=X&ei=r8N6U6zyHMz9oASU4IGgDQ&ved=0CAgQ_AUoAQ&biw=1078&bih=990
