Pectin is a very important part of making jams. It's not often that I'd make some without adding pectin. Here's a list of high pectin fruits that have enough pectin in them to make jam without adding pectin:
Grapes (Eastern Concord)
Plums (not Italian)
Anything else needs pectin to be added. I often hear (erroneously) that strawberries are a high pectin fruit and adding pectin isn't needed. NOT SO! If you have under ripe berries you might be able to get away with it, but under ripe berries taste bad. Under ripe fruit often has higher pectin content than it's ripe version. When I preserve jam made of these fruits, I always add pectin:
Grapes (Western Concord)
I got interested in making jams and jellies without using commercially prepared pectin for a number of reasons. First of all, I am thrifty and it can cost well over $2 per box. Secondly, I just wanted something a little more natural. A pectin factory receives apple residue or citrus peels from juice factories. It's mixed with acid to get all the pectin out of the sludge. The solids are separated and then alcohol is added to precipitate the pectin out of solution. Ammonia is added to some kinds to make it work without added sugar normally needed (those expensive brands of pectin that allow you to make jams and jellies without adding sugar), and then it's mixed with dextrose or sugar to stabilize it. The good news is you can make all the pectin you need with apples and lemons.
Last year, I wrote about how to make your own pectin. Check it out! Happy canning!