These are some of the custom OmniWeb 5 shortcuts I use on a regular basis:

(There is no good export feature, so this is the raw XML code from ~/Library/Preferences/com.omnigroup.OmniWeb5.plist, you can manually add these to that file)

• Amazon: Search all of amazon

 <key>amazon@</key>
 <dict>
      <key>encoding</key>
      <string>application/x-www-form-urlencoded</string>
      <key>formData</key>
      <string>url=index%3Dblended&field-keywords=%@</string>
      <key>format</key>
      <string>http://www.amazon.com/exec/obidos/search-handle-form/</string>
      <key>method</key>
      <string>POST</string>
      <key>name</key>
      <string>Amazon.com</string>
 </dict>

• All Music Guide: Search by artist name

 <key>amg@</key>
 <dict>
      <key>encoding</key>
      <string>application/x-www-form-urlencoded</string>
      <key>formData</key>
      <string>P=amg&sql=%@&opt1=1</string>
      <key>format</key>
      <string>http://www.allmusic.com/cg/amg.dll</string>
      <key>method</key>
      <string>POST</string>
      <key>name</key>
      <string>AMG All Music Guide</string>
 </dict>

• eBay Item Search

 <key>ebay@</key>
 <dict>
      <key>formData</key>
      <string>cgiurl=http%3A%2F%2Fcgi.ebay.com%2Fws%2F&sokeywordredirect=1&from=R8&satitle=%@</string>
      <key>format</key>
      <string>http://search.ebay.com/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.com%2Fws%2F&amp;sokeywordredirect=1&amp;from=R8&amp;satitle=%@</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>eBay items</string>
 </dict>

• FedEx Package Tracking

 <key>fedex@</key>
 <dict>
      <key>format</key>
      <string>http://www.fedex.com/cgi-bin/tracking?action=track&amp;language=english&amp;last_action=alttrack&amp;ascend_header=1&amp;cntry_code=us&amp;initial=x&amp;mps=y&amp;tracknumbers=%@</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>FedEx tracking</string>
 </dict>

• Google Image Search

 <key>gis@</key>
 <dict>
      <key>formData</key>
      <string>q=%@&ie=ISO-8859-1&hl=en</string>
      <key>format</key>
      <string>http://images.google.com/images?q=%@&amp;ie=ISO-8859-1&amp;hl=en</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>Google Image Search</string>
 </dict>

• Google I'm Feeling Lucky

 <key>gl@</key>
 <dict>
      <key>format</key>
      <string>http://www.google.com/search?ie=utf8&amp;oe=utf8&amp;q=%@&amp;btnI=I'm+Feeling+Lucky</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>Google (Lucky)</string>
 </dict>

• Merriam-Webster: Dictionary

 <key>mw@</key>
 <dict>
      <key>formData</key>
      <string>book=Dictionary&va=%@</string>
      <key>format</key>
      <string>http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&amp;va=%@</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>Merriam-Webster Online</string>
 </dict>

• Google News

 <key>news@</key>
 <dict>
      <key>formData</key>
      <string>hl=en&edition=us&ie=ascii&q=%@</string>
      <key>format</key>
      <string>http://news.google.com/news?hl=en&amp;edition=us&amp;ie=ascii&amp;q=%@</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>Google News</string>
 </dict>

• SANS IP port usage: Find out what's going on in your logs

 <key>port@</key>
 <dict>
      <key>format</key>
      <string>http://isc.sans.org/port_details.html?port=%@</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>IP Ports</string>
 </dict>

• eBay Seller Search

 <key>seller@</key>
 <dict>
      <key>formData</key>
      <string>MfcISAPICommand=ViewListedItems&userid=%@&since=7&sort=3&rows=25</string>
      <key>format</key>
      <string>http://cgi6.ebay.com/ws/eBayISAPI.dll?MfcISAPICommand=ViewListedItems&amp;userid=%@&amp;since=7&amp;sort=3&amp;rows=25</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>eBay Seller Search</string>
 </dict>

• UPS Package Tracking

 <key>ups@</key>
 <dict>
      <key>format</key>
      <string>http://wwwapps.ups.com/WebTracking/processInputRequest?sort_by=status&amp;tracknums_displayed=1&amp;TypeOfInquiryNumber=T&amp;loc=en_US&amp;InquiryNumber1=%@&amp;track.x=0&amp;track.y=0</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>UPS tracking</string>
 </dict>

• USPS Package Tracking

 <key>usps@</key>
 <dict>
      <key>encoding</key>
      <string>application/x-www-form-urlencoded</string>
      <key>formData</key>
      <string>CAMEFROM=OK&strOrigTrackNum=%@</string>
      <key>format</key>
      <string>http://trkcnfrm1.smi.usps.com/netdata-cgi/db2www/cbd_243.d2w/output</string>
      <key>method</key>
      <string>POST</string>
      <key>name</key>
      <string>USPS tracking</string>
 </dict>

• Weather.com local forecast

 <key>weather@</key>
 <dict>
      <key>formData</key>
      <string>where=%@&what=WeatherLocalUndeclared&lswe=&lswa=&search=search&whatprefs=</string>
      <key>format</key>
      <string>http://www.weather.com/search/enhanced?where=%@&amp;what=WeatherLocalUndeclared&amp;lswe=&amp;lswa=&amp;search=search&amp;whatprefs=</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>weather.com</string>
 </dict>

• Wikipedia: Internet Encyclopedia

 <key>wp@</key>
 <dict>
      <key>formData</key>
      <string>search=%@</string>
      <key>format</key>
      <string>http://en.wikipedia.org/wiki/Special:Search?search=%@</string>
      <key>method</key>
      <string>GET</string>
      <key>name</key>
      <string>Wikipedia</string>
 </dict>

del.icio.us shortcuts adapted from Us.ef.ul

• See also Mozilla Add-Ons: Search Engines