Guide to docs in this directory: 

ds312.pdf: Spartan3E FPGA Family Complete Data Sheet

sim.pdf: Synthesis and Simulation Design Guide

spartan3e_hdl.pdf: Libraries guide for use with HDL

spartan3e_scm.pdf: Libraries guide for use with schematics

ug086.pdf: Memory Interface Generator User Guide

ug230.pdf: Spartan-3E FPGA Starter Kit Board User Guide

ug331.pdf: Spartan 3 Family User Guide

ug500.pdf: Programmable Logic Design Quick Start Guide

wp321.pdf: HDL Coding Practices to Accelerate Design Performance

wp260.pdf: Memory Interfaces Made Easy with Xilinx FPGAs and the
           Memory Interface Generator 

wp274.pdf: Multiplexer Selection

wp277.pdf: Expanding Dedicated Multipliers

wp335.pdf: Creative Uses of Block RAM

xapp463.pdf: Using Block RAM in Spartan-3 Generation FPGAs

xapp464.pdf: Using Look-Up Tables as Distributed RAM in Spartan-3
             Generation FPGAs 

xapp465.pdf: Using Look-Up Tables as Shift Registers (SRL16) in
             Spartan-3 Generation FPGAs  

XAPP768c.pdf: Interfacing Spartan3 Devices With 166 MHz or 333 Mb/s
              DDR SDRAM Memories 

examples: examples and reference designs from Xilinx