Generally those referred to as "money bills".
Money bills -- legislation that will require the expenditure of public funds, which means the levying of taxes -- can only be introduced by Cabinet. The budget is, of course, the biggie. Money bills also cannot be initiated in the Senate.
The opposition (in the House only, not the Senate) can also always just introduce a specific motion of non-confidence. That could be done if the govt. didn't recognize a defeat on a non-money bill as a non-confidence vote, or if the time just looked good.
Conversely, a govt. can say that it intends to treat a particular vote as a confidence vote -- that it's staking its right to govern on whatever measure it's trying to pass.
This Liberal MP's campaign site gives a good basic explanation (of a few other things, too):
http://www.votelynnmyers.ca/FAQs.htmThe Government must have the support of the House of Commons and retain its confidence in order to stay in power. If the Government should lose a vote on important legislation, or any motion of non-confidence, the Government would be expected to resign or to ask the Governor General to call a general election, according to constitutional convention. This practice reflects the principle of responsible government which makes the Prime Minister and the Cabinet directly accountable to the elected House of Commons and, ultimately, to the people.
Constitutional convention is what really reigns supreme here -- the Queen's just there to enforce it. ;)