Faced with the prospect of having to think up simultaneous equations, I decided to build a spreadsheet to generate them for me,

This spreadsheet (excel), randomly generates pairs of simultaneous equations, with the solution given in (x,y) form.

The equations and solution can be copied in to word documents, reformatted etc.

The spreadsheet produced three combinations of questions:
y = mx + c (two of...)
y = mx + c & ax + by = c
ax + by = c (two of...)

the values of all can be limited using the "range" so you can make them as easy or as hard as you like.