Combine Your Plants

On my "New Items" blog, I came up with the idea of the "Fusion Machine," which will allow two plants (but not upgrades or the Imitater) to be combined into a new plant, therefore only taking up one seed slot. It can only be used once per level. My biggest question about it is: what plant combinations can you come up with? To get started, I have two ideas. First, the Repeater and the Torchwood would make a Flaming Repeater, which will shoot two flaming peas at once. The Frozen Repeater, which is the Repeater and Snow Pea, will shoot two frozen peas.