My two favorites are discontinued. Breyers used to make a fried ice cream flavor that was awesome, and Hagan (a local brand) used to make a flavor called Graham Slam.
since I can't have either of those flavors anymore, I make due with chocolate peanut butter swirl, the one made by Hagan is the best.
I also really like homemade chocolate frozen yogurt, but it's such a pain to make that we don't have it often.
Not technically ice cream, but I 'luv' Culver's chocolate frozen custard, or what's more readily available where I live now - Goodberry's chocolate frozen custard.
That's my favorite too! Technically, it's a sorbet, not ice cream, but I've loved it since I was a kid. I remember once they got rid of it and replaced it with "Margarita Ice" and there was almost a revolt. Daiquiri Ice isn't the most popular, but it's fans are hardcore! Fortunately they brought it back quickly.