I've got the stroke trainer, stroke perfector (both homemade)Joe Tuckers third eye stroke trainer and a Rempe Cue ball.Soon I will add Colin's idea of a laser pointer to the equation....LOL...what can i say I'm a hard core fanatic allways looking for a stroke.
Two things regarding the stroke:
Vision:
Some people don't see center ball were center ball really is. Joe Tucker's third eye is excellent for training your eye to see center ball.
Mechanics:
Proper lineup is essential for straight stroking.A lot of players don't give them self a chance because the are lined up improperly.Here is an article I saved about lineup:
STROKE FLAW CORRECTION
If you have a pendulum and noticed that your stroke pushes slightly outward from your body thus creating a little left, it means that your back leg is situated too close to your grip hand, and the tendency is for the arm to "push" away from the body, much like in golf when you stand too close to the ball which can push the club away from the body spinning the ball to the left (or right if you are lefty). The opposite could happen if your back leg were too far from the stroke hand creating a tendency for the hand to draw in to the body making the tip go to the right.
If your stroke were perfect and you were still putting left on the ball, it would mean that your head is not in the correct position.
Despite the fact that you want to leave out the pendulum debate, please note that it is virtually impossible to have a perfectly straight stroke without one. That is not to say that one is better than the other (althoug it is). But it is altogether possible that your head and aim are perfect but the curve of your stroke makes the tip go slightly right. If this is the case, either aim a little to the right (not suggested) or fix your stroke (suggested).
In summary:
The best way of course to correct lineup flaws is of course with a certified professional(preferably master) instructor.Many of them can watch stroke the ball and in a few minutes give you solutions to set your self straight.
Recentley I've been using the alignment advice I got from Bert kinisters Volume 11, Advanced Fundamentals and I've noticed some good improvement with the combination of that and working with Joe Tuckers third eye.I highly reccomend this particuliar kinister vide

ther's have said the Mighty X(Volume 12) by Kinister further improved their stroke.
With all the gadgets I've made, videos I've watched and alignment drills I've tried I hit the ball reasonably straight today and my stroke is OK.I still need to do the most important step of all and that's spend some time with a certified instructors who may perhaps tweak things a little here and there before I settle in and say I love my stroke.Hopefully I'll make it down to the USA as planned to obtain that instruction because the sort of instruction I want isn't offered locally.
RJ
ps. A proper grip is essential.Gripping the hell out of the cue at impact will also put a bad twist into the stroke. Once again see an instructor.