Can anyone suggest some store procedure exercises for beginners?

You can start with some basic concept of SQL PL / SQL , then start with basic type of stored procedures.

for the same you can select the book from book store are your choice sipply read the book 5 to 10 min and select the book as your need,
following some books/links are good for the basic.
PL / SQL by Ivan bayross
Microsoft SQL Server Black Book
Teach Yourself SQL
A Primer on SQL, 2nd Edition
http://www.java2s.com/Tutorial/SQLServer/CatalogSQLServer.htm[^]

http://msdn.microsoft.com/en-us/library/bb545450.aspx[^]

http://www.w3schools.com/sql/default.asp[^]

Sql Server - How to write a Stored procedure in Sql server[^]

i strongly suggest you to learn this

http://msdn.microsoft.com/en-us/library/ms190782.aspx[^]

See these links..
hope you'll got few store_procedure example and after seeing these i hope you'll create your own.

http://www.aspsnippets.com/Articles/How-to-write-a-stored-procedure-in-SQL-Server-Management-Studio.aspx[^]
http://www.mssqltips.com/sqlservertutorial/162/how-to-create-a-sql-server-stored-procedure-with-parameters/[^]
http://msdn.microsoft.com/en-IN/library/ms345415.aspx[^]
Sql Server - How to write a Stored procedure in Sql server[^]

http://www.onlineexpert.com/elearning/user/pdf/sqlserver/ch11.pdf[^]

For an extra challenge, try out recursion with stored procedures:
http://technet.microsoft.com/en-us/library/aa175801(v=sql.80).aspx[^]