Compiled here is a list of commonly used transaction codes for SAP-BASIS System Administrators, I am currently working on adding further descriptions and explanations (man pages) to attach to every t-code below. If anyone wants to help out with this, please e-mail me.
AL08 Lists current active users – on all the application servers
AL11 Lists SAP Directories on the OS Level for the application server
DB01 Lists applications waiting in a lock-wait or deadlock situation on Oracle.
DB02 Database performance on Oracle
DB03 Displays configuration: parameter changes in database on Oracle
DB05 Analysis of table with respect to indexed fields on Oracle and DB6
DB6BACKHIST Backup and Recovery: Overview
DB6COCKPIT Diagnostics: System Check on DB6
DB6EXL Lists applications waiting in a lock-wait or deadlock situation on DB6.
DB6PARHIS Displays configuration: parameter changes in database on DB6
DB6PERF Performance: Database Snapshot
DB6SPACE Space: History – Overview on DB6.
DB12 Backup logs on Oracle
DB13 DBA planning calendar on Oracle
DB14 DBA logs on Oracle
OSS1 Logon to SAPNet (OSS)
RZ03 Display Server statuses and alerts (all servers)
RZ04 Maintain operation modes and instances
RZ10 Edit/Maintain profiles
RZ11 Display profile parameter maintenance and current values
RZ20 CCMS Monitor Sets
RZ21 Maintain Monitoring: Properties and Methods
SCAT Computer Aided Test Tool: Initial Screen
SCC1 Client copy according to transport request
SCC3 Displays Client Copy Logs / Transport Log Analysis
SCC4 View clients: Overview/ Change client Details
SCC5 Delete client
SCC7 Client import – post processing activities
SCC8 Client export
SCC9 Client Copy: Copy a client (Remote)
SCCL Client Copy: Copy a client (Local)
SCMP View/Table comparison between remote systems
SCU3 Analysis of changed customizing objects and tables
SE01 Transport organizer (extended view)
SE03 Transport organizer tools
SE06 Post-Install methods for Transport Organizer
SE09 Transport organizer
SE11 ABAP Dictionary: Initial Screen
SE15 R/3 Repository Information System
SE16 Data browser: Initial Screen
SE17 General Table Display
SE38 ABAP Editor: Initial Screen
SE80 Object Navigator
SFT2 Maintain public holiday calendar
SICK SAP Initial Consistency Check
SM01 Transaction Codes: Lock/Unlock
SM02 System messages
SM04 User List on current application server
SM12 View lock entries
SM13 View Update Records
SM21 System log: Local/Remote Analysis
SM30 Maintain Table Views
SM31 Maintain Table Views
SM35 Batch Input: Session Overview
SM36 Define background jobs
SM37 View Background Jobs
SM49 Display/Execute External OS Commands
SM50 Lists Work Process Overview in the current application server
SM51 Lists all the instances on the database
SM58 View Transactional RFC Status
SM59 Display and Maintain RFC Destinations
SM63 Display/Maintain Operation Mode Set
SM64 Trigger Event in Background Processing
SM66 System wide Work Process overview
SM69 View/Maintain External OS Commands
SP01 Output Controller: Spool Request selection screen
SP02 Output Controller: List of Spool Requests
SP11 TemSe: Request Screen
SP12 Administration of Temporary Sequential Data
SPAD Spool administration: Initial Screen
SPAM Support Package Manager
SPAU Modification Adjustment: Object Selection
SPCC Spool: Consistency Check
SPDD Modification Adjustment: Dictionary
SPIC Installation Check for R/3 Spool
ST01 Switch on/off, View: System Trace
ST02 Tune Summary, Buffer Stats
ST03 Workload Analysis
ST03n Load Analysis
ST04 Performance: Database Snapshot
ST05 Trace Requests: SQL, Enqueue, RFC, Buffer trace
ST06 Local OS Monitor
ST07 Application Monitor: User Distribution
ST10 Table Call Stats
ST11 Error Log Files / Developer Traces
ST12 Single transaction Analysis, Performance Traces: SQL, Enqueue, RFC
ST22 ABAP dump analysis
STAT Workload: Display Statistical Records for users/t-codes, etc
STMS Transport Management System
SU01 User maintenance: Display and maintain users
SU01D User maintenance: Display user details
SU02 Manually Edit Authorization Profiles
SU03 Maintain authorizations: Object Classes
SU10 Mass User Maintenance
SU2 Maintain User Parameters
SU22 Maintain Assignment of Authorization Objects to Transactions
SU3 Maintain own user parameters
SU53 Display Authorization Data for the executing user.
TALM Database threshold maintenance