I tend to go to sleep while watching movies or TV shows on my computer. I didn’t know of any other way to set your computer to sleep after a given time, so I wrote up a small applescript to do this for me. I thought since I’ve learned so much from MacScripter, I’d give back to the community, so here it is. The input supports a number of different formats, e.g. “1 hour 30 minutes”, “2 h 45 m”, “23 seconds”, etc. Save it as a stay open application. 
set sleepTime to 0
set theText to text returned of (display dialog "Set sleep timer for:" default answer "1 hour 30 minutes")
set defaults to AppleScript's text item delimiters
set AppleScript's text item delimiters to " " -- use " " as delimiters
set theWords to text items of theText
set timesToRun to (number of theWords) / 2
set n to 0 -- index
-- parse time.
repeat timesToRun times
set n to n + 1
set tempTime to item n of theWords as integer
set n to n + 1
set tempWord to item n of theWords
if tempWord contains "h" then -- hours
set sleepTime to sleepTime + tempTime * 3600
else if tempWord contains "m" then -- minutes
set sleepTime to sleepTime + tempTime * 60
else -- seconds
set sleepTime to sleepTime + tempTime
end if
end repeat
set AppleScript's text item delimiters to defaults -- restore default delimiters
delay sleepTime
tell application "System Events"
sleep
end tell