I have a 60D and while I have upgraded to the 24-105mm, 100mm F/2.8L Macro, the 50mm f/2.8, and the 70-200mm f/2.8L USM... I had to slowly climb the ladder starting with the 18-55.
First, I'd suggest buying used or even better refurbished. And if you can be patient, you can get 15-20% off most lenses, and if you are crazy lucky, you can get 30% off great lenses, but I wouldn't hold your breath on those.
Here's a best case scenario (presuming you live some place without tax).
24-105mm f/4L IS for $643. Leaving you with $357.http://shop.usa.canon.com/webapp/wcs/stores/servlet/product_10051_10051_263354_-1
It's not the widest option on a crop sensor, but it is a great lens that is often underrated because of the 24-70 and the performance of primes.
Next, a 40mm pancake lens or the 50mm f/1.8. The 50mm f/1.4 actually outperforms it's L series f/1.2 counterpart, but it can have some AF issues if it takes a fall.
The 40mm pancake can be found for $200 and compares favorably to as the younger brother to some L lenses... Not quite as good, but also 1/7th the price. The 50mm f/1.8 is findable at $100... and is the best value lens out there. It's shallow depth of field can take your shots from simply photographs to pieces of art that should be hung from your walls. At this point.... I'd lean towards the 40mm, but I was sad when I eventually sold my 50mm when I upgraded to the f/1.4. After the $200... you have $157 left.
And finally, I'd suggest getting a 55-250mm IS. It's not ideal for all settings, but for outdoor photography it is an amazing value lens. The 70-300 can be found (if you are lucky) for around $300, but really it normally is around $450 or so. The 55-250 can easily be found for $150 used or even knew (the last one I had to sell was new and I sold it for $170). There are upgrade options, but I don't think they are worth discussing unless you are willing to not get the 40mm and downgrade the 24-105. And you have $7 left to get some cheap hoods from Amazon to protect the glass. I prefer doing that over UV filters.
Now here's the problem, the 24-105 usually sells for around 850 to 800 from ebay without a real warranty. It has dipped to as low as 750. But Canon is sold out and so you are probably out of luck getting it at the crazy amazing price.
But you can get a 15-85mm which is a near tack sharp lens and a great lens for an entry level non L. http://www.amazon.com/gp/offer-listing/B002NEGTTM/ref=sr_1_1_olp?ie=UTF8&qid=1350876853&sr=8-1&keywords=15-85mm+canon&condition=used
You can get a used one for 560 in like new condition leaving you 440 left.
If you get the 55-250 for 150, that will leave you around $300. And then you can possibly find a 50mm f/1.4 for around 300... though $350 is more likely. I wouldn't buy that one used because of the AF issues, but if you buy it new and then put on a hood, I think you are good to go.
And now back