Linear Technologies makes very nice Spice simulator which is a) free; b) reliable; c) updated on weekly basis (so if you experience issues they'll be fixed rapidly) and d) has one of the -- if not the -- fastest, precise and numerically stable solvers (it it recommended to go to Tools->Contol Panel->Spice and choose Solver->Alternate).
One of the major problems with SwCAD is lack of standard elements (though the library of LT chips is quite impressive); you can download my library of elements. Most of them are obtained from respective manufacturers' web cites, some were borrowed from Yahoo LTSpice group, so were provided by private parties. I admit that in the latter case I often slightly modified the schematics so that the element's symbol and other files do not need to be copied into the same directory with the schematics (the path to respective spice library file is embeeded into the symbol), the user does not need to enter model name (it is embedded into the symbol), and, in couple of cases, corrected the problem of using node 0 (global ground) inside subcircuit. Except for these rare and minor changes, I tried by best to retain original files with all the copyrights and references to the part manufacturer and/or circuit owner.