amazon.com has great deals on lenses sometimes.
If you're strapped for cash, a good cheaper lens is the Canon EF 75-300mm. You can find it for around 199.99 in stores, or 120.00 on amazon. It's not IS, and you need a tripod in low/no light shots, and the AF is kind of slow. But aside from that its a good lens that takes good pics, as long as you know its limitations. I just make sure to have my tripod w/ me anytime i MIGHT need it, and i manual focus 90% of the time when i'm using it.
That's on the canon end at least.
EDIT:
as much as i'd love to save for the lifetime purchases only...I needed lenses i could afford now, for the situations i may need them for. Saving money for big purchases is a VERY slow process in my house, so I'm perfectly fine buying a budget lens FOR NOW, so i have a lens for most situations, and then saving for the lifetime purchases later on.
Some will put up with the 15-55 kit lens until they can afford a good lens, regardless of when that is. I would go crazy if i only had the kit lens, so i needed options.
This is a decision thats up to nobody else but you, with pros and cons on both sides. It's about your own priorities and financial situation.