One of my favorite atlernatives to mainstream office products. Open Office is a great alternative as it provides nearly identical features, and the price is what I like as it's free. This provides the basic office tools, Document, Presentations, Database, and Spreadsheet programs at your fingertips.
These are all great tools, that I have used for years, and as of today I can say I've experienved no issues with these programs. I use it in my personal computers as my office tools of choice. Could they be better? Yes, but I could say that same thing about main stream office products as well.
It may not have the "coolest" new UI design, but it has the features I need to do presentations, and it's been a fabulous set of tools to work with.
Now if your looking for a set of office productivity software with a solid name behind it that also free. Then I highly recommend Lotus Symphony. This software is brought to you by IBM. You have IBM standing behind this product, which makes many people at ease that it will be around for the long haul.
This is what I use for my work. My work computers have Lotus Symphony 3.01 installed on it and I use it daily. The feature I love the most, is the export to PDF, you can create a beautiful PDF quickly and easily, straight from your document.
Life is better with free software, whether you decide to go the open source route of Open Office or Lotus Symphony with IBM behind it, you won't be disappointed. You win with either by keeping your precious $$$ in your pocket.