Create a simple AppleScript:
on open (fileList)
set outFile to (choose file name with prompt "Output file:" default name "FileList.txt")
open for access outFile with write permission
repeat with oneFile in fileList
write (POSIX path of oneFile) & "
" to outFile
end repeat
close access outFile
end open
... and save it as an application. To use it, select all in the search window, then drop the list of files on the AppleScript. It can also be used with any other sort of list-of-files-from-the-Finder.
EDIT: If you want to set this up as a service rather than a droplet (and are running Snow Leopard), create this in Automator rather than AppleScript, use the "Service" template, set the "service receives select" pop-up to "files and folders", add a Run AppleScript action, paste in the above script, but with on run {fileList, parameters} ... end run instead of on open (fileList) ... end open. Save it with some appropriate name, and then to use it, select the files, right-click (or control-click), and select Services > yourservicename from the pop-up.