I guess I'm just a little concerned that no-one has yet mentioned the most sophisticated tool known to us: our own brains!
(OK,
mine ain't that great, but . . . . . )
Anyway, it seems to me that if you make widgets, and you sell widgets, then you should have some idea of what the average widget buyer is looking for, and is likely to search for when they come to Google to find a supply of widgets.
If you
don't have any idea . . . . well! - I suspect that
no amount of search engine optimisation is going to save your business.
If you read Dan Thies' piece he offered earlier in this thread, you'll soon realise that, in order to construct the Google AdWords ads that he recommends, you have to have this basic level of insight to begin with anyway.
So, I thought it worth mentioning that there is no substitute for your own expertise in your business.
No amount of software can replicate your experience in running your business in the Real World .
Now it may be that everyone in this forum knows this so well that my mentioning it is embarrassingly redundant. If so, then I apologise.