Logos Bible Software just went to version 3.0. I have been using Logos since the early-mid 90s and this product keeps getting better and better. In my mind this is such an aid to study that it is worth every dollar of the investment.
All the 411 on new features etc. is availabe here: http://www.logos.com/logos3 For all the ESV fans out there, the new Word Study tool is linked to the new ESV-Greek/Hebrew interlinear.
Very sweet. Mac users, let not your hearts be troubled, there is a version in the works