Any way to get the "Open With..." list via AppleScript?
One option would be to use AllApplications in a shell script:

tell application "Finder"
    set p to POSIX path of (item 1 of (get selection) as text)
end tell
set l to do shell script "~/bin/AllApplications -path " &amp; quoted form of p &amp; " | sed 's/.*\\///g;s/\\.app$//g' | sort -f | uniq"
set answer to choose from list (paragraphs of l) without multiple selections allowed
if answer is false then return
set a to item 1 of answer
set p to path to application a
tell application "Finder" to open selection using p


You could also use System Events to get the applications from the Open With menu:

tell application "System Events" to tell process "Finder"
    set l to name of menu items of menu 1 of menu item "Open With" of menu 3 of menu bar 1
end tell
set text item delimiters to linefeed
set l2 to do shell script "grep -vx 'missing value' &lt;&lt;&lt; " &amp; quoted form of (l as text) &amp; " | grep -vx Other… | sed -E 's/ \\([^)]*\\)$//g;s/ \\(default\\)$//g;s/\\.app$//g' | sort -f | uniq"
set answer to choose from list (paragraphs of l2) without multiple selections allowed
if answer is false then return
set a to item 1 of answer
set p to (path to application a)
tell application "Finder" to open selection using p


I didn't really test the scripts, but they're probably affected by rdar://9406282: Finder scripting selection may refer to bogus value not correlated with UI.

Related questions at Super User:


Access Finder's "Open With" menu from the commandline (for tab completion)
Is it possible to query the launch services database for applications that will open an arbitrary file or UTI type?