I'd definately go with the EF 24-70mm f/2.8 L USM over the EF 16-35mm f/2.8 L II - especially in light of currently having a crop frame. The EF 16-35mm f/2.8 L II USM will be a very nice wide angle lense when you move up to a full frame - but on a crop frame it's a bit narrow - I'd hold off on that one until you purchase your full frame (in any case you're likely going to want something to fill in the 35-70mm range anyway, so you won't be disappointed with the EF 24-70mm f/2.8 L USM). I just purchased the EF 24-70mm f/2.8 L USM (for use with 50D) - if you don't absolutely need the 2.8 aperture then another lens you should look at is the the EF 24-105mm f/4 L IS USM (check out the review on this site) - it's a little smaller and lighter than the EF 24-70mm f/2.8 L USM making it a great walk-around lens, and it reaches past 100mm which is nice when you need it, without having to switch to the EF 70-200mm f/2.8 L USM. It happens to be the kit lens for the 5D Mark II - so if you're planning to go full frame you can save a bit by getting them together in a kit. If you need good wide angle coverage on a crop frame then I'd recommend the EF-S 10-22mm f/3.5-4.5 USM - the downside of course is that the lens can't be used on a full frame.