Can't go wrong with Canon's entry level telephoto lens. 75mm-300mm, handles a good bit of abuse, and is inexpensive enough that you're secure taking it just about anywhere.

http://www.amazon.com/Canon-75-300mm.../dp/B00004THD0

It's not the highest quality glass by any means, but many of the shots you see up there (including ALL the airplane shots, both scale and RC) were shot with it.

There's another 'step up' in the canon brand as well. Lenses are a bit faster, less loss of clarity out at the edges, have image stabilization, that sort of thing. You'll pay more, but not outrageously so.

http://www.amazon.com/Canon-70-300mm-4-5-6-Lens-Cameras/dp/B0007Y794O''

Both of those will focus pretty close, and their auto-focus is more than quick enough for even quick airplanes.

I'd also ABSOLUTELY say to grab the canon 50mm 1.8 It's an EXTREMELY nice portrait-quality lens, and has some FANTASTIC glass for the price. You'll REALLY like it for closer stuff, and if you want to shoot any electric/indoor RC stuff.
http://www.amazon.com/Canon-50mm-1-8.../dp/B00007E7JU

And finally, if you REALLY want THE best 50mm lens on the market for the money, imo, that's the Canon 50mm 1.4 It is my favorite portrait lens on ANY camera at ANY price.
http://www.amazon.com/Canon-Standard.../dp/B00009XVCZ


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Having said all that, I'll put this in "real world" terms. Unless there's a very specific reason to carry something specific, 99 times out of 100, I'll leave the house with the 75-300 and 50mm 1.8, and never find myself wishing I had another lens. One of those 2 is responsible for every photograph you see in my first post.