I have a manbag or mag lol and I love it. Mines just plain black leather I bought it from Primark of all places it was only £6 or $12 for all you american guys out there. It's a messenger style, not too big not too small, just average size, looks smart, is useful and handy and I can fit everything I need to take out with me in it, I don't think they look girly at all as long as you buy from a guy range and carry it right as a previous poster pointed out.
I also have a backpack which I also like but I don't always want to carry a backpack around as I live in London and I think it can look a bit touristy, I also find it spoils the look of some of my clothes especially when I'm not dressing in more formal stuff.