Good question. I guess as a kid, it was whatever I thought looked cool. These days I need to be inspired by either the aeroplane's history/performance or the story of the pilot. I often spend more on the books/reference material than the model itself - guessing I'm not alone in this. You guys aren't helping me with inspiration (as in I'm getting too damn much inspiration at present!) - my kit buying is outstripping my model production rate and has for some time I just need to increase build rate and reduce buying rate and all will be good!
Main topics of interest for future builds are:
Late WW2 Luftwaffe - mainly Fw-190, Me-163, Me-262, Ta-152
X-Planes - must build a X-15 sometime - love the "Bull".
Aerobatic aeroplanes - anything I've flown, or had a ride in, or wish to in the future, or just delighted in watching at a air show.
Racers - just cause they're kick ass! I'd like to build some of the historic racers and record breakers as well.
1/32 Fast Jets - Su-27, E.E Lightning, BAE Hawk-127, F-8, F-4C
That list above represents the next 20 year build plan - not in any specific order.