Grackles are not one of my favorite birds, but over the years I have learned to tolerate them. (Unlike European starlings and house sparrows, they're a native species, so it's illegal to kill them!) They really like my yard because it's the perfect habitat for them to nest in -- lots of evergreen trees. I like the evergreen trees because they grow pretty fast and they provide lots of shelter and nesting spots for other birds too. In addition to the grackles, I have had robins, mourning doves, cardinals, and brown thrashers nesting in them. (Unlike starlings and house sparrows, the grackles also never compete with my cavity nesting birds for nesting sites.)
Grackles tend to dominate the bird feeders. I think this is partly because there are so many of them, plus they are a somewhat pushy bird. A few summers ago I watched a grackle peck a house sparrow to death. I had never seen that before and I've never seen it since. Both birds were eating on the ground, and for whatever reason when that house sparrow got close to the grackle, something just made that grackle attack and kill the house sparrow. I wasn't too upset because I like house sparrows even less than grackles. It was just shocking because it was so unexpected.
I have the advantage of having a big yard and am able to put designated "grackle feeders" farther away from the house, so they're less likely to come and eat from the feeders where I want to see the "nice" birds. Grackles are somewhat lazy and will go to where it's easiest for them to find food.
For my grackles feeders, I rely heavily on the open tray feeders and fly-thru feeders. In these feeders I put a blend that attracts the grackles: black oil sunflower, cracked corn, and some white proso millet. The advantage is these seeds are less expensive and in addition to the grackles, many other birds will also eat it, including mourning doves, cardinals, bluejays, and sparrows.
The other thing I do to keep grackles away from feeders where I don't want them is to put guards on my tube feeders. Then I can put out the good seed for my little birds who can get through the guard: chickadees, house finches, chipping sparrows, and even the downy woodpecker. The only disadvantage to these guards is that it restricts the larger birds. For the tube feeder closest to my dining room window, I'm going to switch to straight safflower seed instead of putting it inside the guard. Grackles don't really care for the safflower seed -- the shell is too hard for them to make the effort to crack and eat the seed inside. This should work out well, because cardinals and rose-breasted grosbeaks will readily eat safflower seed. That way I can still see those birds up close.
So, spring is here and with it grackles. I guess it's something I'm just going to have to live with as a backyard bird feeder. While they don't have a pretty song or even very pretty feathers, they do eat lots of insects in my yard, and for this reason alone, I will tolerate them for a few months each summer.