I just today found out about something that was in plain sight in the Books Online... but the documentation is so vast, I haven't discovered everything yet.
I blogged about clearing a single plan from cache in SQL Server 2005 a while back, and mentioned a rumor that there would be a new way to do this in SQL Server 2008. And then just today, someone posted a comment on that blog post, asking about the new 2008 method.
One of my contacts on the SQL Server team at Microsoft just sent me an email telling me about new features related to plan caching, as I am starting to work on updating that chapter for my 2008 book. He mentioned that DBCC now takes parameters, and one of the parameters is a plan handle!
DBCC FREEPROCCACHE [ ( { plan_handle | sql_handle | pool_name } ) ] [ WITH NO_INFOMSGS ]
There is full example in the Books Online, so I won't repeat it here. If you don't have a local copy of BOL handy, you can read about the new option to DBCC FREEPROCCACHE online here:
http://msdn.microsoft.com/en-us/library/ms174283.aspx
Have fun!
~Kalen