I'm in pretty much your boat exactly-- engaged and keeping my maiden name for the reasons you've specified. My fiance has mixed feelings about the matter, but he understands my position and has essentially said that he'll get over it.
As far as our family is concerned, we're going to give any kids his last name. I'm going to stick my last name in there as a second middle name if I have any say in the matter (and I do). That's what my fiance's parents did to him and his brother and they haven't had any issues with it.
I think you have two valid options, given the details you've supplied:
1) Do what my fiance and I are doing,
or
2) hyphenate anyhow and let the kids pick their last names when they're older-- middle or high school aged-- and then encourage them to change it legally (or not, depending on their choice) AFTER they turn 18.
There are a few reasons I would discourage you from just having them take your name. The first is that people are waaaaaay more wary of men dealing with small children that don't have their last name than they are of women. Someone mentioned picking kids up from camp, and that was a good example of where this can come up.
The second is that it will affect the way your family is viewed. If a mother and her kids have different last names but they still call her mom, people will assume they got their dad's last name. If a father and his kids have different last names, it doesn't matter if they call him dad or not-- most people will assume that they aren't his, at least not biologically. I would ask your boyfriend if that kind of assumption would bother him to figure out if this is a major consideration for the two of you.
Good luck figuring all this stuff out-- then again, maybe when you have a kid everything will just fall into place for itself.
