One style of tattoo which is popular for both genders is the tribal tattoo. Again, there isn't a particular gender-oriented style but female tribal designs lean more towards the curvy, flowing style than the more spiky, thorny look of one a man might favour. Often the female tribal design will intertwine with vines, flowers or butterflies, resulting in a feminine yet 'tough' look which can be extremely attractive, if inked well and in a good location on the body.
Tribal tattoos for women tend to use lighter and/or thinner lines, and often have 'sparkly' embellishments to them. Quite often they will form an abstract picture of a heart or animal, as opposed to a man's tribal tattoo which is often just a non-specific pattern.
Of course, there is no hard and fast rule when it comes to tattooing, and I mean no disrespect to anyone by attempting to stereotype any particular tattoo design. At the end of the day, a tattoo is a personal choice and it's entirely down to your own personality as to what tattoo you choose. I myself have several tattoos, some of which could be classed as 'manly', others which are more typically feminine. Remember, a woman can get away with having masculine tattoos a lot easier than the reverse!