Software download: http://www.linear.com/designtools/software/#LTspice

1. Short but effective guide to LTspice at ltwiki.org
2. Switcher CAD 3 manual, the last official manual by Linear Technology of the LTSpice IV predecessor. Mostly used as reference.
3. Great tutorial by Gunthard Kraus, e.g. lossy transmission lines, S-parameters, filters, …
4. RF Special Edition: Complete Simulation of a 137MHz Weather Satellite Converter using LTspice IV by Gunthard Kraus
5. Tspice IV Getting Started Guide, Linear Technology presentation
6. Undocumented LTspice
7. Simulating Ideal Opamp
8. LTwiki: Courseware and Tutorials

• LTSpice - Voltage Controlled Switch (youtube video)

A short tutorial is the LTSpice Parameter Sweep Tutorial by Andrew Herdrich, Department of Electrical and Computer Engineering, Portland State University, January 7, 2007, Version 2. The examples below are taken from that tutorial.

Parameters and parameter sweep are defined by directives (commands starting with at dot).

Constant parameter:

.param C=1uF

Common loop expression, e.g. to test capacitors from 1μF to 10μF in 2μF steps:

.step param C 1uF 10uF 2uF

Parameters from a list:

.step param C list 0.47uF 1uF 2.2uF 10uF

Logarithmic (common log, base 10) parameter variation, e.g. 8 steps from 100nF to 1uF:

.step dec param C 100nF 1uF 8

logarithmic (base 10) AC sweep from 1 Hz to 100kHz with 10 steps per decade:

.ac dec 10 1 100k