Tyler Hamilton nicely summarizes the available incentives for installing tankless water heaters, drain-water heat recovery systems (here are two examples), and solar hot water heaters.
Many of the rebates and incentives are time-limited, so it's worth considering for this year. (If you are an Enbridge customer, here's a link to their rebate page.) However, he also notes that the Ontario government is musing about low- or no-interest loans for solar hot water. So, if you need to borrow to pay for your system you might want to keep that in mind.
I also received a flyer from Sears that says they now rent tankless water heaters, as well as drain-water heat recovery systems. We plan to call to get a quote, so when we get more info on that we'll pass it along.