Flashy

So, I have an Amazon gift card that I want to use on photography stuff. Here are my thoughts:

Some sort of flash or flash filter so I don't just keep taking yellowy grainy pictures inside and whatnot.

OR

A new lens. Macro? Telephoto? Something I don't know about yet?

What do you all recommend? My gift card is only $50, but that doesn't mean I can't spend more! :)