Excel is certainly packed with features, but I use a few free add-ins that make Excel even better.
[Update] I've created a list of all the free Excel add-ins that were suggested in the comments. Thanks for sharing your favourites!
by Jan Karel Pieterse of JKP Application Development Services
If you use names in Excel, you need this tool. You can quickly find names with errors and delete them, or track names that link to another workbook. There are many more features, so download Name Manager, and see what it can help you with.
by Rob Bovey of AppsPro
Rob's add-in has handy tools for working with named ranges, worksheets and selections. You can quickly protect and unprotect all the sheets in a workbook, remove unused styles, and my favourite – centre across a selection, without merging cells.
There are many more features, and you can read the full description on Rob's page for Excel Utilities.
Since I work with pivot tables so often, I created my own pivot table add-in, that you can download.
The commands that I use most often are Clear Old Data, and Sum All Data.
Your Favourite Free Excel Add-Ins
What are your favourite free add-ins for Excel? Any of the ones that I've listed? Have you created some of your own?