Another comparison, EF-S 17-55 F2.8 IS usm vs ef 17-40 F4L

[ilzho]

Ok, i need to make another decision between the 2 for my 'everyday' lens and landscaping.

EF-S 17-55mm f 2.8 IS USM vs

EF 17-40mm f 4 L

I friend told me to get the 'L' series as I would not need IS at this range for the most part.

[ilzho]

You're right.

My brother let me have one of his Speedlite 580 EX II external flash.

I haven't used it, but it will be essential to learn and use.

[Waddizzle]

"Be warned, though, that you may have to buy a flash unit, if you don't have one already." 

You would want a flash, anyway.  I have found onboard flashes to only be good for fill flash in a pinch.  It seems the only lens that doesn't cast a shadow are very small ones, like pancakes and the 18-55mm kit lenses they pack into T5 kits.