Is it quite common at most Orthodox shuls for there to be a women's shiur presented by a female? What topics would generally be discussed?
It's hard to say what's true of "most" Orthodox synagogues, but certainly most I've been in have classes for women presented by women, yes. Topics have included Scripture (parashas hashavua or Nach), hashkafa (Weltanschauung), halacha (often related to the time of year), and others: basically most of the non-textual topics covered by men (who speak for men or for women or for mixed crowds). Occasionally they have been based on texts (usually excerpts photostatted and distributed) and covered halacha or similar topics more analytically, especially in more 'modern' synagogues.
I don't think I can do a survey and tell you what percentage of shuls have classes for women or classes that are open to men and women. My Young Israel has both, and the classes for women are taught either by women or by our rav or another of our many local rabbis.
I think whether or not a shul has classes for women, and the level that the class is taught at, depends upon supply and demand. If there are many women in the shul who want to learn more -- especially those with a background themselves having gone to day school, or Stern College, and/or seminary in Israel, there is great demand and so long as there are teachers who can teach the subject, synagogues respond to the demand and begin classes. I have heard of shuls that only teach women courses on cooking, taharas mishpacha, and basic Shabbos in the kitchen halachas. But there are so few examples of those that I've encountered, I'm more inclined that a majority do have at least classes open to men and women. Some even have Talmud shiurim open to women, and these are not necessarily the "modern" shuls. Rabbi Phillip Rabinowitz, zt'l, the Polish-born Orthodox rabbi who had received smicha at what is now called the Skokie Yeshiva, was the rabbi of Kesher Israel Congregation in Washington, D.C. In the early- to mid-1970s, the congregation's membership was mostly older, less educated Jews, many of whom were not shomer Shabbos. The baal t'shuva movement on campuses soon changed that for the better, but in the 70s, there was an Israeli woman who wanted to attend his Shabbos afternoon Talmud class but was reluctant to sit at the table with the men. Instead, she sat in the back of the beis midrash. Seeing her interest in learning, the Rabbi had his daughter sit in on all of the classes so that this women (and later others) would be comfortable. A former neighbor of mine, a Holocaust survivor, had a similar story about her experiences in pre-war Poland. She also stood at the door to hear the rav teach Gemara to the young men. The rabbi saw that she was more attentive than the boys and probably retained more. From then on he had her sit next to him at all of the shiurim.