This site details it well:
There's an Ontario tab on there too, unfortunately that page doesn't appear to be as succinct.
Anything that was charged both GST and PST before will be charged full HST now (the changes to rounding may cause total taxes charged to be off ±1¢ on any given purchase). Anything that was exempt from GST remains fully exempt from HST. There are also some new things fully exempt from HST; see the link above. Anything that was exempt from PST but was charged GST will now be charged full HST, except the following items which only pay the GST portion of it:
* Gasoline, ethanol, diesel and bio-diesel when used in motor vehicles as well as locomotive fuel used for trains, marine diesel used for boats, and aviation fuel and jet fuel used for aircraft.
* Children’s-sized clothing and footwear
* Children’s car seats and car booster seats
* Feminine hygiene products