Some popular entry level models:
Giant Defy 3
Trek 1.2
Specialized Allez
Scattante R-330
Fuji Newest 3.0
For entry level prices, I would prefer to buy used from craigslist. You can get some pretty good bikes for that price, and for many used bikes, it's not that hard/expensive to fix it up. Or you could get a used steel bike with downtube shifters for less than half of that price. That way, there's less risk of getting it stolen. Steel is more comfortable for the rough roads and downtube shifters are easier to maintain. A quality steel bike will not be much heavier than aluminum (for those climbs).