I've just seen a treecreeper (Certhia familiaris) from my office window! I've not seen one for at least 10 years so I'm pretty excited. These are fantastic little birds that climb up vertical tree trunks, using stiffened tail feathers for support.
Here's a lovely photo from Arkive (which if you haven't seen it before is a collection of wonderful photographs of (mainly) endangered species). For more information about these birds, see the RSPB page