Haskall et al., The effects of L-theanine, caffeine and their
combination on cognition and mood, Biol Psych (2008); 77: 113–22.
Here's some of the detective work I've done:
The principal investigator of this study is listed on your link on ClinicalTrials.gov as Andrew Scholey of Northumbria University.
Looking on Google Scholar, and searching with the key terms "Andrew + Scholey + Caffeine" and looking for publications after the study's 'actual completion date', as listed on ClinicalTrials.gov, I found an article by Scholey & coworkers, namely:
Haskall et al., Biol Psych (2008); 77: 113–22.
The study doesn't mention 'ClinicalTrials.gov Identifier: NCT00487227' explicitly, but given the study's senior author (Scholey), the publication date (2008) being a few years after the clinical study's completion date (2005), and the topic of the paper (cognitive effects of caffeine) that closely resembles the clinical trial's topic, I bet this is the article you're after.
Otherwise, I should simply contact Scholey - most researchers appreciate an email enquiry about their work. More often than not they're eager to spread their work across the scientific community.