SharePoint List Column Limits

There are limits in number of columns we can create in a SharePoint list. You may Get "Column Limit Exceeded" when You add a new column to a SharePoint List. This is because of the column limitations.

For SharePoint 2003/2007:
With Windows SharePoint Services, you can create the following numbers of each column type for each list or library:

•     64 Single line of text and Choice (drop-down menu or radio buttons)
•     31 Multiple lines of text and Choice (check boxes (allow multiple sections))
•     32 Number and currency
•     32 Hyperlink
•     16 Date and time
•     16 Lookup
•     16 Yes/No
•     8 Calculated

Refer this KB for the limitations on the maximum number of columns we can have:
http://support.microsoft.com/kb/823555

The above applies to SharePoint 2007 as well, but This is not a hard limit.

For SharePoint 2010 lists Column limits:  
Refer this Technet article: http://technet.microsoft.com/en-us/library/cc262787.aspx#Column