Here are some quick ones for later:
What are the state of sip registrations:
asterisk -rx "sip show peers"
Have stuck channels - i.e. call won't hang up?
asterisk -r pbx*CLI> core show channels Channel Location State Application(Data) SIP/EXT-blahhhhhh couch Up Dial... channel request hangup SIP/EXT-blaaaah
Have a need to reload sip?
asterisk -rx "sip reload"
Performance testing dahdi fake timing source:
http://www.cadvision.com/blanchas/Asterisk/DahdiPerformanceTesting.html
In case it goes away:
dahdi_test ... Run for 5 min minimum... Acceptable values range from 99.975% to 100%. With values lower than 99.975%, you can expect problems. Check for irq conflicts.