Joel Oleson and Steve T provide this great list of Performance Counters for SharePoint.
Replace the server name $fe1$ with your front end and $be1$ with the back end server name.
Front End Perf Counters
\\$fe1$\Processor(_Total)\% Processor Time
\\$fe1$\Process(LSASS)\% Processor Time
\\$fe1$\Process(w3wp)\% Processor Time
\\$fe1$\Process(OWSTIMER)\% Processor Time
\\$fe1$\Memory\Pages/sec
\\$fe1$\Memory\Pages/sec
\\$fe1$\Memory\Available Bytes
\\$fe1$\System\Context Switches/sec
\\$fe1$\Process(w3wp)\Working Set
\\$fe1$\Process(w3wp)\Private Bytes
\\$fe1$\Process(w3wp)\Page Faults/sec
\\$fe1$\Process(w3wp)\Working Set
\\$fe1$\Process(w3wp)\Working Set Peak
\\$fe1$\Process(w3wp)\Virtual Bytes
\\$fe1$\Process(w3wp)\Virtual Bytes Peak
\\$fe1$\Process(w3wp)\Private Bytes
\\$fe1$\Process(w3wp)\Page File Bytes
\\$fe1$\Process(w3wp)\Page File Bytes Peak
\\$fe1$\Process(OWSTIMER)\% Processor Time
\\$fe1$\ASP.NET\Request Execution Time
\\$fe1$\ASP.NET\Request Wait Time
\\$fe1$\ASP.NET\Requests Queued
\\$fe1$\ASP.NET\Requests Rejected
\\$fe1$\ASP.NET\Worker Process Restarts
\\$fe1$\ASP.NET\Application Restarts
Back End (SQL Server) Performance Counters
\\$be1$\\Processor(_Total)\% Processor Time
\\$be1$\Memory\Pages/sec
\\$be1$\System\Context Switches/sec
\\$be1$\Process(sqlservr)\% Processor Time
\\$be1$\Process(sqlservr)\Working Set
\\$be1$\Process(sqlservr)\Private Bytes
\\$be1$\SQLServer:General Statistics\User Connections
\\$be1$\SQLServer:Databases\Transactions/sec
\\$be1$\SQLServer:Locks(_Total)\Number of Deadlocks/sec
\\$be1$\SQLServer:Locks(_Total)\Lock Waits/sec
\\$be1$\SQLServer:Locks(_Total)\Lock Wait Time (ms)
\\$be1$\SQLServer:SQL Statistics\Batch Requests/sec
\\$be1$\PhysicalDisk(_Total)\Current Disk Queue Length
\\$be1$\PhysicalDisk(_Total)\Disk Read Bytes/sec
\\$be1$\PhysicalDisk(_Total)\Disk Write Bytes/sec
Links to the TechNet capacity planning content for WSS and MOSS 2007 can be found in this post.
Thanks Joel!
