Q:

How to achieve that hoppy aroma and top notes

Me and my brewing buddy have been brewing beers for some years now, we are pretty satisfied with our end products. Hardly any of that yeasty taste that can be quite prominent with home brews. 
We normally use dry hopping to try to achieve that hoppy nose known from many professional IPAs, this does however fall flat most of the time. We are looking for that aroma you can get with some beers that is reminiscent of the ones you get when opening a bag of hops, hoppy and fresh. 
Does anyone have any suggestions for how to achieve that in a home brewing context? 

A:

I think the primary factor would be how much you're dry-hopping with. More hops means more of the volatile aromatic compounds that produce those aromas.
Most of the recipes I've seen call for somewhere from 1 to 4 ounces of hops in the fermenter but I've heard of people using as many as 10+ ounces for dry-hopping. I'm not sure how that matches up with what commercial breweries use but it seems like the obvious place to start.
That said, ensuring you have fresh, high-quality hops is also important. Try to keep up on when your LHBS gets new hops in and try using what's fresh, that may make a big difference as well. Similarly, the quality could vary between producers. If you can get hops from different brands/farms that may also make a big difference.
Other considerations could be yeast strain and water chemistry. Certain yeast strains and higher sulfate content can help accentuate hop character.
I would recommend taking a look at each of these variables and experiment to find what works best for what you want out of your beer.

A:

In addition to the other answers which I agree with. 
Late boil additions are very important too at last 1-5 minutes or whirlpool. These add a "deep" aroma for lack of a better term.  They seem to bond to the wort at this temp and hang on through fermentation. 
Dry hopping in early fermentation while does add aroma and flavor tends to have much of it blown off in cO2 escape. But is still an important step in hop bombs.
Late dry hopping with fresh hops is where you get most of your aroma 3-7 days before cold crash and well past most cO2 blow off from fermentation.
Applying all three of these in your hoppy beers will give you that complex layering of hop aroma found in most commercial examples.

A:

From my experience thesquaregroot got it mostly rigtht - fresh hops and sufficient quantity.
There is one more really important factor. As far as my experiments go, 4 days before adding hops and bottling are optimal. Any more or less time means less aroma - it either didn't dissolve in your beer yet, or already started to evaporate. And never, ever dry-hop when your ale is still bubbling!

