Jeff,
I did ask this question a while ago here and got some suggestions.
Ultimately I ended up with the following:
An Original GradeMaster Card Centering Tool (eBay)
A blacklight flashlight (Amazon)
A loupe that has both a blacklight LED and a regular LED light 10x (Amazon)
A DS-3 Magnifier (Amazon)
So all this stuff above is overkill for sure, but I am somewhat anal too.
I rely on the GradeMaster Centering tool to get a really good idea as to how well the centering T/B/L/R both front and back.
The blacklight flashlight is to look for surface scratches that I cannot see with my nekkid eye.
The loupe with the blacklight lets me see any up close imperfections and any corner problems that I cannot see otherwise.
The DS-3 magnifier has a light in it as well and just serves as an additional aid.
I also have a 30x magnifier (oversize acrylic) that comes in handy at times. (Amazon)
And then, above all else, I hope the TPG sees the same things as I do.
Because frankly the graders are better at this then I am by a huge margin.
This provides me with data that I use to determine if I want to send a card to the TPG (exclusively SGC) to have graded. Ultimately their decision wins obviously.
And then there are some cards that I just do not care about and I just get graded regardless of condition. That is strictly my decision.
Hope this helps some....
Butch