Claymore
Dogs
Dogs: Bullets & Carnage
Raiders

My all time fave is Tokyo Crazy Paradise (which was mentioned earlier) cause it has a great action and fighting scenes, with a slight supernatural twist, and there is a very definite romance 😉

Others I like are:
Erementar Gerad (lots of action, a more obvious romance that is a main part of the story, and amazing art)
Double Arts (although it got cut short earlier than planned, it still had a very unique battle style thats worth a read, also has romance)
Soul Eater (similar battle style to erementar gerad, but has a very creepy-yet-still-smooth looking setting to it)
Rave (intense battles, more similar to One Piece rather than Bleach, also has romance, which ties in to make for a very epic ending, although its slowly developed like most shounen-romances)
Fairy Tail (same author, no romance that i can see)
Blazer Drive
Black Cat
Shaman King (a longer series, but still worth a read, not much of a romance story though)
Marchen Awakens Romance
Tsubasa Reservoir Chronicles (an action romance, but its also heavily revolved around the 'tragedy' genre it has)

There are also some series that arent action-based, but still includes fighting and whatnot:
Yanki-kun to Megane-chan (a delinquent/school based type of action)

From the manga: Good Luck, Demon King!