I thought for my first blog, I would grab something I posted in a forum a few years back troubleshooting alerts.  I had to go back and read these over a few weeks ago to troubleshoot alerts not working on our one farm.

• Things to check when Alerts are not working:
• Verified Alerts are enabled (set alerts-enabled to false, then back to true.)
• tried stsadm -o updatealerttemplates -url "http://client" -filename "c:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\template\xml\alerttemplates.xml"
• tried STSADM -o setproperty -pn job-immediate-alerts -url url -pv "every 3 minutes"
• tried sts add-on stsadm -o restarttimer
• tried using sts add-on stsadm -updatealerts as client has web server https:// and app server http://, so  to do a search and replace of https with http and vice versa (alert propertybag setting).
• added the account used to run the SharePoint Timer Service as SharePoint Administration Group account (farm admin).
• Made sure the account used for OWSTimer.exe had read/write access to the Content Databases and SQL.
• verified account that the SharePoint Timer Service is running under does have access to the content database
• Re-entered username and password of Timer service account, stopped, started
• rebooted the servers (web, app, and db)
• Looked in WSS_Content and other content db's and looked in ImmedSubscriptions, schedsubscriptions for anything out of the ordinary.
• Looked in log files and this message appears.
• break permissions of site, then list/doc lib, then re-inherit.
• Ran vb script to test message to verify the configuration of the SMTP service (http://technet.microsoft.com/en-us/magazine/cc718983.aspx)
• Make sure your server is allowed to send out email (at my one client, the network guys didn't allow the one SharePoint server to send email
• Make sure your outgoing email server is allowing email from your SharePoint severs (issue I had recently).