Yes, but for the money
this one is better.
Also consider the
Sigma 530 - Bwana & Koffie have it.
I have the Super, and yes, you want the Super. Is similar in power and features to the Canon 580EX line, but cost half the money.
The 50D is a big camera - not sure if you're going to need the grip - go for the flash first.
There's a lot of body to hold on to. If I was doing portraits every day without a tripod, I'd invest in a grip. But for the odd photo now and then, it's not necessary.
You can't bounce a 50mmf1.8 off the ceiling. Well...
I'll bet you R1400 you can
I have a concern though, do all the Canon lenses work on all the Canon SLRs - I read hat the EF-S range is dedicated to SLRs with an APS-C size sensor?
Like bwana said. EF work on all bodies (DG in Sigma terms - I'm not sure what the other manufacturers call it), while EF-S (DC in Sigma terms) work only on the 1.6x crop sensors (not on the 1.3x).
My feeling is that, if you know you'll be getting a full frame camera in the next few months, and you know for sure you'll do away with your crop body, don't make it too much of an issue. Use your common sense. For some things there are alternatives. If you know you will definitely move to a FF cam soon, and you can get by on 28mm at the wide end, then a 28-200 FF obviously preferable to an 18-200 crop lens. But if you want a wide to medium zoom like the 18-55, then you have no choice.
In my case I already have a FF body (film) but my 24-105 is more than wide enough for it. I am in the market for a faster 18-55-ish, so I'm definitely going to get the Canon EF-S 17-55 f/2.8, which won't work on the film camera or on any future FF DSRL, but I'm buying it to use *now* - no some undetermined time into the future. And I know when I do get my 5DmkII (or whatever is out then), I'm not planning on doing away with the 40D, unless it breaks. The value that I will have derived from the lens will be enough to satisfy me.