The following Python script cycles through your Twitter timeline and takes the most recent Tweet that fits certain critera.
It will only show tweets that do not include a @reply, a link or a hashtag. It then displays the Tweet as a Quote, neatly divided over as many lines as is necessary, with all HTML entities replaced by their respective Unicode characters, and the name of the poster appended neatly underneath.
Demo

Installation.
Get your API details from Twitter. Twitter has a set of documentation that walks you through this process. Fill in the form on the Twitter developer site and you will receive a CONSUMERKEY, CONSUMERSECRET, ACCESSKEY and ACCESSSECRET.
Add these details into the text below where they are requested and copy/paste the script into Notepad.
Save as TweetQuote.py. Make a note of the path.
Load Terminal and type: 'easy_install tweepy' without the quotes. (tweepy powers this script, if this install fails then you may need to install setuptools for Python)
Add the following as a GeekTool shell command
'python /Users..[insert full file path here]../TweetQuote.py'
Script
import tweepy, os, sys, re
# Declare OAuth varibles.
CONSUMER_KEY = '...'
CONSUMER_SECRET = '...'
ACCESS_KEY = '...'
ACCESS_SECRET = '...'
keyfile = "authkeys.dat"
auth = tweepy.OAuthHandler(CONSUMER_KEY, CONSUMER_SECRET)
auth.set_access_token(ACCESS_KEY, ACCESS_SECRET)
api = tweepy.API(auth)
# Break string into multiple lines
def para(text):
return reduce(lambda line, word, width=50: '%s%s%s' %(line, ' \n'[(len(line)-line.rfind('\n')-1
+ len(word.split('\n',1)[0]) >= 50)], word), text.split(' '))
# Convert html entities into Unicode
def unescape(text):
def fixup(m):
text = m.group(0)
if text[:2] == "&#":
try:
if text[:3] == "&#x":
return unichr(int(text[3:-1], 16))
else:
return unichr(int(text[2:-1]))
except ValueError:
pass
else:
try:
text = unichr(htmlentitydefs.name2codepoint[text[1:-1]])
except KeyError:
pass
return text
return re.sub("&#?\w+;", fixup, text)
# Script
type = api.home_timeline(count=30)
for result in type:
if result.text.find('@')==-1 and result.text.find('http://')==-1:
twtu = result.user.screen_name
twtt = result.text
print para(unescape(twtt)) + "\n" + "\n- " + twtu
break