You've got that right, i'm trying to decide on a prime that will give me a good wide angle on the cropped sensor, as well as a standard zoom. Kind of caught up in all of the rumors now, and hoping a 24-70 2.8L II shows up soon. Been eyeing up the 16-35 2.8L II, the 24 1.4 II, the 35 1.4, and the 24-70 2.8L. I have also been looking at zeiss primes, but i think for certain situations i will prefer autofocus, leading me to believe i will be sticking with a canon prime.
Technically, 'wide angle' means 35mm or shorter on FF, therefore 22mm or shorter on APS-C. Thus, the only Canon primes that will give you a wide angle on APS-C are the EF 14mm f/2.8L II and the EF 20mm f/2.8 USM (also, the EF 15mm f/2.8 Fisheye, but you're probably looking for a rectilinear lens). The 24mm lenses come close (just barely in the normal range), but the 35mm f/1.4L is absolutely a normal lens on APS-C.
In fact, with an APS-C sensor you'll get better IQ with the high-end EF-S zooms (17-55mm, 15-85mm) than their approximate FF L-series equivalents (24-70mm and 24-105mm, respectively) when comparing on the same APS-C body. Also, the high end EF-S lenses hold their value quite well. For example, although I still have my 17-55mm, I sold my 10-22mm when I bought a 5DII and 16-35mm II, and after nearly a year of use I only lost $50 on the sale of the lens. That was before the round of price hikes earlier this year - currently, used prices for the 17-55mm are running around what I paid for the lens brand new, although since it optically outperforms the 16-35mm II on my 7D (better resolution and less CA), and
has IS, I'm holding onto the 17-55mm as a general purpose lens for the 7D.
Personally, I think it's better to get the lenses best-suited to the body you're currently using, and worry about a possible FF upgrade when you are actually making that upgrade. That's especially true depending on the lens(es) you plan to get - for exmaple, if you're looking at the 24-105mm, that's much cheaper in the 5DII kit, and during the spring and fall lens rebate programs, rebates on some lenses are often doubled when you buy a body at the same time.
Primes are a different story, in that there's only one EF-S prime. But even with L primes, you'll have a different lens if/when you get a FF body so it's tough to pick a single focal length that works as you want on both formats.