I'm a fan of always sticking with OEM. Minus lenses lol We've all got a couple of Sigmas and Tamrons and they're all real decent, however once you get into some longer zoom lenses off-brand, they become a bit slower and dont focus as well and arent typically as sharp. You may want something a little more towards the wide angle. Most of us have the Sigma 10-20, but there are lots of options for that range. But if you wanna go wide you're looking at another 400+ easily...

As for the flash, pick up a 430!