Good lens for Rebel XTI

[kirkaz]

First off, I know nothing.

Taking a cruise at the end of June to Alaska. We have a Rebel XTI, with just the stock lens. Looking for an upgrade that would be superior quality shots of scenery and what not.

I don't want to go to crazy price wise, but I would rather get something good and spend some money, rather than be disappointed later....Lets say $500 or so.

Thanks for any help.