I use TinyUrl and the Wikipedia bookmarklet more than any others: javascript:(function(){q=document.getSelection(); if(!q){void(q=prompt('Wikipedia keywords:',''))}; if(q)location.href='http://en.wikipedia.org/w/wiki.phtml?search='+escape(q)})()

Here's an amazon.com lookup one as well: javascript:void(q=prompt('Enter%20text%20to%20search%20Amazon.',getSelection()));if(q)void(location.href='http://www.amazon.com/exec/obidos/external-search/?keyword='...(q)+'&mode=blended&tag=blogography00-20&Go=Go')