I like to go planespotting at the local airport now and then. We don't get the biggest planes, the biggest planes in regular traffic are 737's and A321's, but it's still good fun. I use my Canon 18-200mm f/3.5-5.6 IS lens for planespotting. It gives me decent telephoto reach, but I still sometimes wish I had a 70-300 for that extra 100mm at the telephoto end. But the place where I spot I'm so close to the planes when they taxi I really need the 18mm to get them in frame, so the 18-200 is actually pretty perfect for the planespotting I do at that airport.
I tried to go planespotting in twilight/dark and it was pretty difficult. I really had to push the ISO to the max and underexpose at least one stop, and even with the help of the IS only a few shots came out good. It's in these situations you wish you had a 70-200 f/2.8 IS! But you can still get some cool pics when the sun's not set completely, like this:
I usually shoot in RAW, but since my buffer fills pretty quickly I tend to switch to jpeg when trying get pics of a touchdown, like this: