Unfortunately the phpBB search engine is a little lacking, and it wasn't something I wanted to spend the entire day on, so the way I've gone about the search is entirely unscientific and necessarily crude, however it's of some amusement value perhaps to see what the results were:
Oil
8146 matches: oil
Unsurprising perhaps, the bald term 'oil' was a really rather too broad, however a more specific search for oil grades revealed:
276 matches: synthetic
112 matches: 10w30
72 matches: 10w
51 matches: 20w
44 matches: 0w20
30 matches: 15w40
26 matches: 15w
23 matches: 5w20
21 matches: 20w50
3 matches: 20w40
14 matches: 10w40
1 match: 15w30
1 match: 20w30
So, from this do we conclude synthetic 10W30 to be the winner? Note the search engine didn't like '/', so anyone using say '10/30' as a term wasn't counted.
Coils
3564 matches: coils
In my view this is probably the most genuinely popular term here. The word isn't used a lot with regard to anything else in a Model T except for the wooden trembler coils, so I think we can be reasonably sure that these coils are a hot topic.
Timer
2987 matches: timer
Coils are closely followed by 'timer', another hot topic. I didn't drill down into timer types as one or two utilise common names that also appear in the forum, however it's clearly one of the most commonly discussed items here.
Starter and generator
3728 matches: starter
2498 matches: generator
Sticking with the electrics 'starter' was ahead of 'generator' by more than 1000 entries. I guess a starter is arguably a more controversial subject, whereas the poor old generator just sits there and does it's thing, until it doesn't?
Pump
1895 matches: pump
This had to be a popular term and I wasn't disappointed. Given we don't have an oil pump, and 'tyre pump' had a fairly low count I think this simple term gives a fair idea of the interest in water pumps ('water pump' returned 876 matches, but as quite a few people shorten it just to 'pump' during discussion this meant adding 'water' tended to lose some relevant posts).
Bands
1779 matches: bands
Closely following pump, 'bands' were another term well up there. It was interesting to drill down a little
408 matches: cotton
540 matches: kevlar
'Scandanavian' returned just two, and I think the term 'wood' was probably to wide. As you can't set a specific term with the phpBB search engine 'wood bands' doesn't work especially well.
12 volt
1410 matches: 12 volt
739 matches: 12v
Back to the electrics and we see that 12v comes up quite a lot. More controversy?
Light bulbs
1005 matches: led
778 matches: bulbs
150 matches: filament
Haha, another favourite topic - and LED surpasses the broad term 'bulbs' by a reasonable amount, but even more so than 'filament'. More controversy perhaps, but maybe LEDs are eventually winning the war...
Regulator and cutout:
831 matches: regulator
592 matches: cutout
I was a little surprised to see that 'regulator' trumped 'cutout' by a good number. Perhaps it was something to do with the 'diy regulator' thread, but neverthless good to see people are clearly aware of regulators - even if it's less certain they might know why they're a better thing than cutouts

Alternator
435 matches: alternator
Another very surprising result, I really didn't think this would return as many times as this. Perhaps worth some more investigation as there could be another reason for this.
And a few more random searches of things that pop up from time to time. I would have liked to include the 'FACT' coil tester too but searching for 'fact' gives obviously useless results. Anyway I should think Mike would be justifiably happy to see 'ecct' up there. Also good to see that 'diy' gets some hits.
819 matches: hcct
476 matches: ecct
573 matches: diy
No doubt there's many more terms one could look for, and you could get quite a lot more sophisticated with the search mechanism, but this should do for the moment I expect. What do think?