Hi avlsi,
I personally use WinSPICE3 from
http://www.winspice.co.uk- It is an extremely good version of spice for designing small mos based circuits.
- It has compatibilty with the "standard" Hspice models provided by most foundries.
- It uses a "C" like scripting language which allow you to control multiple simulations.
The really nice thing about WinSPICE3 is its ability to read each device instances' model, then write back new values to those individual device models - not something you can do in any of the big commercial simulators (I won't mention them here as I don't want to be flamed!). If you have an interest in doing detailed device level design of analogue or RF cells such as op-amps or mixers, you will find WinSPICE3 extremely useful.
Another really nice touch is that it "remains resident" - this means that at the command line (in the window it runs in) you can interactively read/print/plot node voltages or device currents or device parameters (or even write to them, then resimulate).
It also means that for (say) optimization of a model, you can use an excel macro to read a CSF output file from WinSPICE3, then write a new (text) simulation file which WinSPICE3 will detect has changed, then automatically re-runs the simulation.
The down side is that there is a "learning curve" associated with learning to use it and it does struggle converging large circuits with totem pole logic in them.
There is a free evaluation version and a nominal charge for the full version which is if you are a budding ASIC designer is well worth paying as you get access to the full BSIM models and the Hspice features.
I also use Hspice (with whose performance WinSPICE compares very favourably) but Hspice is very, very much more expensive and hardly qualifies as "spice @ home" for anyone but a true "spicer".
LTspice has some nice features like the ability to read schematics from other schematic entry tools such as Pspice and Cohesion, but it tends to be targeted at the PCB/system/discrete fraternity.
Happy Sims,
SimonH.