Amy Ziari, Pasta founder here. There are plenty of great agencies out there. The best list I know of is O'Dwyers. For example, its list of top tech PR agencies: http://www.odwyerpr.com/pr_firm_rankings/hightech.htm
"Top" is based on annual billings vs. quality, so the list is something you'd want to supplement with recommendations and research. Still, it's a healthy starting point.
