The one software package we couldn't do without lately is Adobe Photoshop 8 Professional.
More and more specs and plans are being delivered electronically in PDF format. It makes it easier to read the specs and plans and more than 1 person can be working with them at the same time. You can also highlight important sections and search the document for those nasty buzz words that we have been taught to look out for. Plus with the ability for more than 1 person to access it, someone can be working with it in the office while other peole can work with it when they are on the road
We also use it for takeoffs and it interfaces well with CAD. The quantities can be exported into our Excel Estimating Spreadsheet.
It's also good for file management. We are experiencing rapid growth and we struggled with a file management system that everybody could figure out (My partner has serious ADD and dyslexia

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You can also use it to prepare presentations. I am beginning to like it better than Power Point