I prefer to spend time preaching through an extended piece of text, but I have only once had the opportunity to spend several weeks in the same book. When I teach my youth I take my time, but that is a whole different monster, since most of the are biblically illiterate (thats another post).
Once I have my text down, and I usually shoot for at least for a few related verses, if not an entire literary segment, I gather my resources. I am a huge fan of Oak Tree's softwares Accordance, and I use it throughout the process. I translate the passage from the original languages first. I don't do this because I want to have my own translation, but instead to see subtle word play and to hopefully spark some good ideas. Some of my best sermons came from things I found once I translated the text. I have a few lexicons inside accordance that I use too, and I bring them out when anything seems interesting or different from the usual english translations (NRSV, NIV and the NLT are my usuals).
Once I have my translation I spend a few hours thinking about the text structurally and theologically. I do some basic level IBS, but I do not go as far as I would for a school assignment. It is in this stage that I often find what I want to focus on. I try to be honest and not take the text outside of it's greater scriptural family or to present it in a way that wouldn't make sense to its contemporary readers/hearers.
Two of the places that I having been going to lately are, "Theological Interpretation of the Old Testament" and its partner "Theological Interpretation of the New Testament", edited by Kevin J. Vanhoozer and published by Baker. I recieved both of these free at SBL last year and I find myself going to them often. Theological Interpretation is a movement that seeks to rejoin the academic families of Biblical Interpretation and Theological studies. It may seem surprising to you that they are separated, but inside the academy, this is a new and innovative movement. It seeks to read the scripture theologically. These books do a great job at showing a wide breadth of theological thought regarding the Bible.
By this time I try to have some themes worked out. I now go to The Essential IVP Reference Collection software that I have for Accordance. I like this set of dictionaries (which can also be found in paper copies) because in Accordance I can surf around the different dictionaries. Its almost like going to Wikipedia, but you can trust (and cite) the information found. It is a quick way to get around alot of information, and I never do any work without it. It is a pretty important tool to me. I really like the Dictionary of Biblical Imagery, The New Dictionary of Biblical Theology and the Dictionary of the Latter New Testament and its Developments the best. I would buy Accordance just for this set.
When I have a couple of things that have really jumped out at me, I look for some academic articles surrounding the topic. I rarely actually use anything from them, but they are a great way to see how others have put together the information. I also have a couple of commentary sets I go to every time (the Sacra Pagina and the Ancient Christian Commentary on Scripture), and then I start pulling things off the library shelf.
By now I have my sermon pretty much outlined and I start trying to put it all together. My pastor usually tells me I need more illustrations, but I strive for a more narrative approach so I have a hard time with stories that are outside of my life. I never speak more than 25-30 minutes so I have alot of triming to do, but I like having the information in front of me. I speak from a manuscript that I am really familar with. I outline my sermon and then annotate the manuscript with the outline. I would say that I don't need it 65 to 75% of the time, but it is nice to keep me grounded.
Well, thats how I prepare a sermon. You need to tell us now as well.