User Administration:

SU01 – User Maintenance
SU01D – User Display
SU02 – Maintain Authorization Profiles
SU03 – Maintain Authorizations
SU05 – Maintain Internet users
SU10 – User Mass Maintenance
SMLG – Maintain Logon Group
SUPC – Profiles for activity groups
SUIM – Info system Authorizations
PFCG – Profile Generator
PFUD – User Master Data Reconciliation

Client Administration:

SCC3 – Checking Client Copy Log
SCC4 – Client Administration
SCC5 – Client Delete
SCC7 – Client Import Post-Processing
SCC8 – Client Export
SCCL – Local Client Copy
SCC9 – Remote client copy

Database Administration:

DB01 – Analyze exclusive lock waits
DB02 – Analyze tables and indexes
DB12 – DB Backup Monitor
DB13 – DBA Planning Calendar
DB15 – Data Archiving: Database Tables

Transport Management System:

STMS – Transport Management System
SE01 – Transport and Correction System
SE06 – Set Up Workbench Organizer
SE07 – CTS Status Display
SE09 – Workbench Organizer
SE10 – Customizing Organizer
SE11 – ABAP/4 Dictionary Maintenance
SE16 – Data Browser
SE80 – Repository Browser
SM30 – Call View Maintenance
SM31 – Table Maintenance

Background Jobs Administration:

SM36 – Define Background Job
SM37 – Background Job Overview
SM39 – Job Analysis
SM49 – Execute External OS commands
SM62 – Maintain Events
SM64 – Release of an Event
SM65 – Background Processing Analysis Tool
SM69 – Maintain External OS Commands
Spool Administration:

SP01 Output Controller
SP11 TemSe directory
SP12 TemSe Administration
SPAD Spool Administration

Other Administration Tcodes:

AL11 – Display SAP Directories
BD54 – Maintain Logical Systems
OSS1 – Logon to Online Service System
SALE – IMG Application Link Enabling
SARA – Archive Management
SICK – Installation Check
SM14 – Update Program Administration
SM35 – Batch Input Monitoring
SM56 – Number Range Buffer
SM58 – Asynchronous RFC Error Log
SM59 – RFC Destinations (Display/Maintain)
SAINT – SAP Add-on Installation Tool
SPAM – SAP Patch Manager (SPAM)
SPAU – Display modified DE objects
SPDD – Display modified DDIC objects
ST11 – Display Developer Traces

Daily monitoring TCodes:

AL08 – Current Active Users
SM12 – Display and Delete Locks
SM13 – Display Update Records
SM21 – System Log
SM50 – Work Process Overview
SM51 – List of SAP Servers
SM66 – System Wide Work Process Overview
ST22 – ABAP/4 Runtime Error Analysis
ST01 – System Trace
ST02 – Setups/Tune Buffers
ST04 – Select DB activities
ST05 – Performance trace
ST06 – Operating System Monitor
ST10 – Table call statistics
ST03 – Performance, SAP Statistics, Workload
SU56 – Analyze User Buffer

Other Monitoring Tcodes:

OS01 – LAN check with ping
RZ01 – Job Scheduling Monitor
RZ03 – Presentation, Control SAP Instances
ST07 – Application monitor
STAT – Local transaction statistics

Other Useful Transactions Codes:

AL22 – Dependent objects display
BAOV – Add-On Version Information
SA38 – ABAP reporting
SE38 – ABAP Editor
HIER – Internal Application Component Hierarchy Maintenance
ICON – Display Icons
WEDI – IDoc and EDI Basis
WE02 – IDoc display
WE07 – IDoc statistics
WE20 – Partner profiles
WE21 – Port definition
WE46 – IDoc administration
WE47 – Status Maintenance
$TAB – Refreshes the table buffers
$SYNC – Refreshes all buffers, except the program buffer