Err, I have a 20D, not a 5D (I wish!).

As for lens choices, IS only helps with shaking, but is still useless in low-light. Both lenses are slow (F-stop number) especially at the long end. The 18-55 is 5.6 at full zoom.

If you're planning on using this camera for travelling, my advice is don't take two lenses. You'll keep having to change lenses at bad times. I'd recommend taking a single lens and lightening your bag. If you don't mind non-canon lenses the Tamron 18-250 looks good (http://www.qualitycamera.com.au/product_info.php?cPath=253&products_id=4159) also there's rumours of an IS version from Tamron but I couldn't find it. If you prefer Canon They've just released an 18-200 with IS (http://www.dpreview.com/previews/canon%5F18%2D200%5F3p5%2D5p6%5Fis/)

A good place to find out more: http://photography-on-the.net/forum/index.php