Then you need much more than $2000, till then you should prioritize.
But a good start would be a Tamron 28-75 for walking around and a Canon 70-200 f2.8 or a f4L for tele work. Next could be a macro, super wide angle, or a super tele.
I live in Iceland, and lenses are very expencive here, so I just buy online from B&H in USA, with shipping, customs and taxes, I still save about 30-40% :)
If you buy the Tamron 28-75 and the Canon 70-200 f4L, the total US price should be about $900. If you want wideangle coverage, Tokina 12-24 or Sigma 10-20 DC is about another $500 for a total of close to $1500 with shipping. If you prefer Macro, then a Canon 100mm or a Tamron 90mm f2.8 are about the same price as the wideangles as well.
I understand that the Sigma 2.8 is pretty good, but you might want to consider carefully going with a sigma instead of a Canon. It is said that Canon stuff works better with Canon cameras. I don't know if anyone with some actual hands on experience could comment on the difference in practical terms of the Sigma 2.8 vs the Canon 2.8.
