Column validation is a new feature of SharePoint 2010 and can be quite valuable to ensuring consistently correct information when adding items to a list.

So that's all well and good, but what about the formulas that we can use for validating our columns?  What and where are they?  First of all, they're based off of the data-calculation formulas that work in Excel, so that should help those of you that are familiar with Excel formulas.  Second, not all Excel formulas are supported by SharePoint.  You'll want to keep in mind that Excel is Microsoft's powerful data calculation application, while SharePoint is a "jack of all trades."  Finally, here's the link to the supported formulas for SharePoint 2010.  It's my understanding that these will work for both Calculated Column types as well as Column Validations.

Have fun validating your data!

UPDATE – 01/18/2015

Here’s a link that gives you an introduction to calculate columns:  http://office.microsoft.com/en-us/sharepoint-foundation-help/calculate-data-in-lists-or-libraries-HA010379916.aspx