Rather than manually having to check all the SQL servers across the environment, I have utilised replication, perfmon counters, little known system procs and scripts to monitor various aspects of multiple servers - for a fraction of the price of commercial products.
Combine the output of these with Reporting Services and you can soon knock up your own dashboard to give an at a glance view across all the servers.
None of these routines are rocket science, and I'm sure most of them could be improved, but you may find some of them useful.
(Once I've got round to putting them up that is)
Logshipping
Custom logshipping code (pre SQL 2005 but works on any, this was written to utilise native backup plus winzip, or RedGate's SQLBackup) and monitoring
Jobs
Monitor for failed and long running jobs, and custom alerting and notifications to multiple users either regarding the job as a whole or individual steps
CPU
Log perfmon counters directly into SQL and analyse for trends
Diskspace
Log free disk space directly from SQL, and analyse for trends and alert if appropriate
Database Size
Monitor database growth, analyse trends, and alert if appropriate
Server / Service availability
Check SQL Servers are up, and that the SQL Server and SQL Agent services are running
Backups
Check the last time SQL backups were done for each database
