Some commands you should know about:

dwho [Weyr] Riders/Dragons currently connected.
pair <rider|dragon> Dragon/rider pairing info
dtulist [color|weyr] List all dragons, or certain colors or weyrs

Specific to Ista are the following commands:

qcensus Shows the online residents
census Shows the online residents
groups wings Breakdown of all the riders by wing
groups ledgelist All the riders by ledges
groups everyone All Istans, grouped by riders/crafters/candidates/

roster weyrlings
roster candidates
roster sphinces
roster phoenices
roster griffons

roster ledges <name> * Find the ledge information on rider *
roster ledges <dragon> * Find the ledge information on dragon *

inews gives you a list of these commands and a few others.