I’ve pretty much eliminated butter from my diet (aside from the occasional store-bought cookie). There are two main products I use in place of butter on bread, bagels, or when cooking/baking, and they both serve their purpose quite well.
The first, I’ve mentioned before: Spectrum Naturals’ Essential Omega Spread. Consistency-wise, it does well on toast and it doesn’t taste all that bad. It does have kind of an odd fishy smell to it (though the Omega-3s come from flax seed oil), but it doesn’t take long before you forget the smell’s even there. It can’t be used for cooking, but it’s mighty fine on a morning bagel.
The second I’d heard a lot about, but only recently tried: Earth Balance spread. This stuff is amazingly like butter, but with none of the trans-fat. It’s by no means health food (it does have a bit of sat fat), but it’s still a great choice if you’re looking to avoid butter. It tastes great, melts perfectly on toast and bagels, and can be used in baking and cooking with good results. And it’s not terribly expensive, either. I haven’t tried any of their Smart Balance line, yet.