To start with Oracle SOA here are some of useful links:

Oracle SOA Suite general

• Oracle Application Intergration Architecture
• Oracle Fusion Middleware (functional)
  
• Oracle Fusion Middleware (technical)

• Oracle Application Server: WebLogic

• Oracle SOA Suite
• Oracle BPEL
• Oracle Service Bus (OSB)
• Oracle Enterprise Service BUS (ESB)

• Business Rules
• Business Activity Monitor
• Business Process Analysis

• Oracle Data Integrator (ODI)

• Oracle SQL Modelleing
• Oracle SQL Developer

Oracle SOA Suite software

• Oracle WebLogic Server

• Oracle SOA Suite
• Oracle Service Bus (OSB)

• Oracle AIA Foundation Pack
• Oracle Data Integrator (ODI)

• Oracle JDeveloper
• Oracle SQL Modelleing
• Oracle SQL Developer

• Patches can be obtained via Oracle Support (Metalink)

Oracle Application Integration Architecture

• The concept of AIA
• AIA Foundation pack
• AIA Process Integration Pack

Documentation

• Oracle FMW 11g
• The Administration Guide
• The BPEL Developers Guide
• The ESB Developers Guide

• The OSB Manual
• The OSB Upgrade Manual

• The Adapters Guide
• The Workflow Guide

• Business Rules User Guide
• Business Rules Reference

• Oracle JDeveloper 11g
• General oracle documentation
• BPEL Correlation
• SOA Suite 10.1.3.3 docs
• SOA Suite 10.1.3.3 New Features
• Best practises 10.1.3.3

• Oracle Database 11g

Installation

• Installation Guide
• ESB Performance patch
• SOA/BPEL patches
• General (Metalink -> Patches -> Advanced -> Product (SOA)BPEL)

Performance

• BPEL Tuning
• Tuning in a nutshell
• SOA Monitor performance

API

• BPEL Process Manager
• Worflow API
• Business Rules
• ESB API

• FMW 11g SDK
• FMW 11g ADF

Tutorials

• SOA Quick start guide
• SOA Tutorial (ESB/BPEL/Rules/Workflow)

Oracle Blogs

• HELP blog
  
• Matt Wright'Blog
• Antony Reynolds Blog
• Clemens' SOA@oracle blog
• AMIS SOA blog
• IT-Eye SOA

Oracle Forum

• Oracle SOA
• Oracle BPEL
• Oracle AIA

Oracle General

• Oracle Technical Network (OTN)
• Oracle Metalink (Support)

Useful tools

• SoapUI
• XML/XSLT/XPath/XQuery
• Test Online XPath (1)
  
• Test Online XPath (2)
• Business Process Modeling Notation (pdf)
• BPMN Visio Stencil (zip)

Webservice standards

• Service component architecture (SCA)
• BPEL
• WS-Addressing
• WSDL
• SOAP
• XPath
• XQuery
• XSLT
• XPath
• WSIF