Canon uses the EF-S mount now
This is not entirely correct.
Canon uses the
EF mount and the EF-S mount. The
EF-S mount is only found on their APS-C (crop-sensor) DSLRs made after the original Digital Rebel (20D, 30D, 40D, 50D, 7D, Rebel, XT, XTi, XSi, T1i, T2i, XS)
The
EF mount is found on all of their full-frame and 1.3x APS-H digital SLRs, as well as all EOS film cameras and a select few older 1.6x APS-C digital SLRs (EOS D30, D60, 10D).
EF lenses can be used on full-frame, 1.3x APS-H, as well as 1.6x APS-C.
EF-S lenses can ONLY be used on 1.6x APS-C and will not physically mount on a full-frame or APS-H camera with an EF mount.
Except for a few specialized lenses (TS-E, MP-E), ALL Canon EF lenses made since the introduction of the EF mount in 1987 have a built-in focus motor. All Canon EF-S lenses also have a built-in focus motor. Many of Canon's midrange and high-end lenses have very fast and silent ring-ultrasonic focus motors that allow for quick focusing and instant manual overrides.
In fact, there's more of these AF-S lenses than I had realized, so IMHO the D5000's lack of a built-in focus motor is not as crippling as it used to be back when the D40 was released.
There are still a few notable omissions, though. The following are some of them:
10.5mm f/2.8 Fisheye, 24mm f/2.8, 28mm f/2.8, 50mm f/1.8, 85mm f/1.8, 85mm f/1.4, 105mm f/2, 135mm f/2, 180mm f/2.8, 80-200mm f/2.8, 80-400mm f/4-5.6.
Nikon has pretty much caught up on their zoom lenses in terms of implementing focus motors, but they still have a lot to do on their fixed-focal length primes.
The lack of a built in focus motor precludes the use of older lenses that can be found very inexpensively on the used market. A couple of notable ones are the Tamron 17-50mm f/2.8 (first version) and Tokina 80-200 f/2.8 (which can be found for as low as $300 these days)
By the way, while it is fully possible to manual focus these lenses, it is not exactly the easiest thing to do, especially with the small pentamirror viewfinder on a D5000. Also, for fast primes (which represent most of the lenses lacking focus motors), the camera's focusing screen can't even show DoF past f/2.5, so you're basically guesstimating focus or waiting on the focus confirmation dot. This can be useful if you have a very static subject, but is a lot more cumbersome than using AF when your subject is moving (even slowly moving).
I've used a D300 at work exclusively with a manual focus lens (an 8mm fisheye), but an 8mm fisheye has so much depth of field that it doesn't require focusing once set to the hyperfocal distance. A lens like an 85mm f/1.8, however, would be a much harder beast to deal with if you were forced to manually focus it on a DSLR with a focusing screen not optimized for manual focus.