Most rats do like the company of another rat. If it is possible, getting your rattie a littermate (or another rat that your rat lived with before) would make introducing a cagemate easier. It doesn't have to be a rat its met before, as long as you take care when introducing them. The following articles should give you some tips on safely introducing rats:

Introducing New Rats
<http://www.ratfanclub.org/newrat.html>

Rat Introductions
<http://www.suite101.com/article.cfm/pet_rats/24945>

Introducing Rats to New Companions
<http://www.rmca.org/Resources/aintro.txt>

Good luck!