American IPAs are supposed to have from 40-70 IBUs. Many commercial examples stick to the lower end of this spectrum, Brooklyn IPA has 45 IBUs for instance. IPAs with lower IBUs (40-50) are more likely to do better commercially since most people don't like crazy amounts of hoppiness in their beer.
However, many beers do well on the higher end of this spectrum. Dogfish Head's 60 Minute IPA has 60 IBUs (fitting), Bear Republic's Racer 5 has 75, and Stone's IPA has 77.
Keep in mind that IPAs are not just about bitterness, you also want the right flavor and aroma from your hops as well. Bell's Two Hearted Ale is not extremely bitter, but is well regarded in the style because it has good hop aroma and taste.
I would say your best bet is to run to your local beer store and pick up a variety of IPAs to do some research. Many breweries will list the IBUs either on the bottle or on their website. Taste a few of them and decide just how bitter you want your final beer.
Final note: Some beers venture into the 80+ range for IBUs but that is generally seen in double or imperial IPAs where there is more malt to balance out the bitterness. If you plan on making a 7% beer I would stick between 40-70 unless you REALLY like bitterness.