I have provided hundreds of indexing examples in the Performance forum.
Here's a sampling of what might be some of the better ones:
index design -
http://forums.mysql.com/read.php?28,558435 (Backup and trimming data idea)
*, index, InnoDB -
http://forums.mysql.com/read.php?22,530328 (Does LIMIT 1 without ORDER BY ID bring the record with minimum ID?)
2-field index -
http://forums.mysql.com/read.php?10,519675 (problem for selecting range of date between 2 dates)
index -
http://forums.mysql.com/read.php?10,519897 (Creating an Index)
EXPLAIN, index, RoT -
http://forums.mysql.com/read.php?10,519097 (Help optimizing query/index)
covering index -
http://forums.mysql.com/read.php?115,514321 (Strange performance with JOIN/COUNT)
index-10-30 -
http://forums.mysql.com/read.php?24,508243 (MySQL 5.1.49 - Optimal settings for memory usage)
index -
http://forums.mysql.com/read.php?10,508224 (indexing)
*, INDEX, not using index -
http://forums.mysql.com/read.php?115,507723 (Problem with a query performance)
bulk, char vs int, index -
http://forums.mysql.com/read.php?10,505513 (Best primary key or index)
indexing -
http://forums.mysql.com/read.php?20,505046 (Issues with possible duplicate indices on table)
compound index, key_len -
http://forums.mysql.com/read.php?24,452643 (Multi-Column indexes)
datatype storage, index -
http://forums.mysql.com/read.php?125,433419 (physical bytes)
index details -
http://forums.mysql.com/read.php?20,433282 (how index grows in size)
indexing -
http://forums.mysql.com/read.php?10,433373 (Looking for understanding of optimizing queries)
prefix index -
http://forums.mysql.com/read.php?10,424725 (Very slow sort on Order By for MySQL query.)
compound index -
http://forums.mysql.com/read.php?24,422437 (Index on Datetime Col is not used When Where Clause combines two or more predicates)
index -
http://forums.mysql.com/read.php?115,418955 (Stop using filesort)
index join -
http://forums.mysql.com/read.php?24,411522 (ideal indexing for inner join, rowcount of 1)
index -
http://forums.mysql.com/read.php?21,409094 (Table marked as crashed and last (automatic?) repair failed)
index, subquery -
http://forums.mysql.com/read.php?106,409897 (Partition on day of year)
index design -
http://forums.mysql.com/read.php?24,409053 (MySQL not using indexes)
index -
http://forums.mysql.com/read.php?24,401240 (11 millions records : more than 30 seconds to retrieve simple request)
index -
http://forums.mysql.com/read.php?24,399387 (Slow query with order by and limit)
index -
http://forums.mysql.com/read.php?10,393815 (Index recomendations)