Data Collection and Statistics Analysis

I'm trying to find an application that will SNMP poll my routers and calculate statistics a little more complicated than the simple average in MRTG. For instance, other than a mean average, I'd like to see a break-up in percentiles -- especially the top percentiles. Does anyone have any suggestions of a program that will do this? By the way, I'd like to stick to UNIX for the polling and analysis platform. Thanks in advance for any help!!! John Zollo