In personal experience, it's been cockscomb celosia and non-stop begonias :). That said, what makes them romantic is the thought that went into them...my husband knows that I love taking care of plants, and I love having green things all through the house. When he wants to buy me flowers, instead of buying me cut flowers that will die quickly he does some research to find out which ones will work well in our house and then buys me some compatible potted flowers from the local greenhouse. The aforementioned flowers were given to me because a) he knows I love non-stop begonias and b) he knew I wanted something with lots of pretty colors for a window box to put into the kitchen. That made those particular ones doubly romantic because not only did he go to the trouble to make sure they would be able to thrive in this house, but he had also been listening closely to our conversations and remembered the information for weeks before finding me the exact right flowers.