If your SQL Server instance encounters the following conditions, a mini-dump is created in the SQL Server LOG folder:

1. Non-yielding scheduler (SQL Server 2005 and above for the first occurrence. This is equivalent to a 17883 dump in SQL Server 2000.)
2. Non-yielding resource monitor (SQL server 2005 and above for the first occurrence)
3. Non-yielding IOCP listener (SQL server 2005 and above for the first occurrence)
4. Deadlocked Schedulers (SQL server 2005 and above. This is equivalent to a 17884 in SQL Server 2000.)
5. Exceptions/Assertions
6. Database Corruption
7. Latch Timeout
8. Other conditions (eg: when DUMPTRIGGER is used to generate a dump for a particular exception)

The first 4 conditions are documented under the following whitepaper:

How To Diagnose and Correct Errors 17883, 17884, 17887 and 17888

In the SQL Server Errorlogs, you will see a message which will indicate which of the following conditions listed above resulted in the generation of the dump. You can use the KB Article mentioned below to list the stack using the Public Symbols with the help of WinDbg:

Use the Microsoft Symbol Server to obtain debug symbol files

http://support.microsoft.com/kb/311503

Addendum: April 14, 2011

Paul Randal wrote a blog post on how to download a PDB file using symchk utility which is installed along with Windows Debugging Tools:

http://www.sqlskills.com/BLOGS/PAUL/post/How-to-download-a-sqlservrpdb-symbol-file.aspx