Registries are incredibly organized and helpful, and it is not "greedy" to register. Most wedding guests find registries a very efficient way to select a gift that the couple would like, would need, and that wouldn't be duplicated by other guests. While it's okay to have more than one registry, draw the line at three. You want to be helpful by offering your guests variety, not self-indulgent by listing your every wish in the world.
The best registries have a mix of both prices and types of items, so that all of your guests will feel comfortable finding something they will be excited to give you. It's fine to have a less traditional registry - one with gardening equipment or camping gear - but include a traditional one, too, even if it isn't very full. Many guests, especially older ones, will feel much more comfortable with a few classic options. At least one registry that has a brick-and-mortar store are also a good idea, for less Internet friendly guests. As shower gifts are typically less expensive than wedding gifts, it might be a good idea to set up a shower registry separate from your wedding registry with lower-priced items, especially if there is a shower theme.
It's also okay to set up honeymoon registry (as one of your "up to three" registries). Where possible, describe how different contributions will be used: "$80: rental car for a day of Rob driving us through the hills of Tuscany." Donation registries are also fine, but draw the line at anything controversial. A local food bank, yes; a political candidate, no.
Let guests know by word of mouth and on your wedding website. Be sure to tell your close family and wedding party where you are registered, as they will likely be asked. Don't include any registry or gift information on the wedding invitation or any of the enclosures. (Some stores will send you preprinted enclosures with your registry information; these are fine for showers, whose purpose is the giving of gifts, but not for the wedding invitation. Some online registries will also encourage you to share your registry on social media--don't do this.
Just remember: In the end, the choice of gift is always up to the giver, so great-aunt Edna might still buy you a blender.