ABAP Hints and Tips: For ABAP/4 programmers to find hints and tips on programming with SAP's ABAP, useful function modules, and source code.
CT-Software: Searchable ABAP Freeware Pool
SAP Development: Provides ABAP source code and information on SAP's technologies.
SAP-EDI.com: EDI/ALE answers in plain English.
SAPEdit: External ABAP/4 editor for SAP. Download, order online.
SapPoint: Documents and screencams on topics of ABAP/4 programming
The SapFaq: Email-based peer-to-peer technical support from experienced professionals. Home of the original MIT-sponsored SAP-R3-L Technical Support Forum. Free to qualified professionals. [Membership required]