I always say that Logos saved my life in seminary. It saved my marriage. It saved my sanity. It saved... you get the point. I can not recommend this resource to pastors or Bible study leaders enough. While I still love a good library full of leather bound books, Logos saves so much research time. Seminarians, you cut and paste from a resource and it will add the citation for you. You can even format which format your school makes you use. Yes, it's a bit pricy. However, it is worth the investment.
The Iphone App makes it that much more amazing. I'm sitting with a leader at a local coffee house. We're discussing a certain Greek Word in 2 Timothy. I click on it in the IPhone app and it pulls up the Greek Word, allows me to do a Word study, and gives me access to various resources--Brilliant!