After a monstrous bull run of late, the stock market finally started to pullback. The Nasdaq Biotechnology Index (NASDAQ:IBB), for instance, fell by nearly 7% last week alone:

IBB Price Chart

Even so, it's important to keep the magnitude of this week's drop in perspective. This leading biotech index is still up by 28% over the past year, and the correction among healthcare stocks in the second quarter has been far steeper than that:

IBB Chart

As a value investor, I am always keen on buying my favorite stocks at discounted prices. Honestly, though, I haven't been buying much lately because prices have gotten ahead of fundamentals, in my view. And despite the drop across the board during the week, prices, to me, still appear to be on the high side. 

With this in mind, I would strongly consider buying Acadia Pharmaceuticals (NASDAQ:ACAD), Gilead Sciences (NASDAQ:GILD), and NPS Pharmaceuticals, (UNKNOWN:NPSP.DL)if the market goes into a full blown crash. Here's why. 

Acadia Pharmaceuticals has a mega blockbuster on its hands
For me to buy a stock as prices plummet, I have to be reasonably comfortable that the company's core business prospects are going to be strong over the long haul. Acadia fits that bill nicely, in my opinion.

My investing thesis in this stock centers around Acadia's experimental treatment for Parkinson's disease psychosis, or PDP, called Nuplazid (pimavanserin). This is a condition with really no treatment options beyond supportive care, which is why the Food and Drug Administration recently bestowed a "breakthrough therapy" designation upon Nuplazid. Acadia is planning to submit Nuplazid's New Drug Application to the FDA before year's end, putting it on track for a potential approval by mid-2015.  

Given Nuplazid's strong late-stage trial results and the need for new therapies for PDP, I think the regulatory risk is minimal going forward, making this stock's value proposition worth checking out. Acadia presently sports a market cap of roughly $2.5 billion, yet experts believe Nuplazid could see peak sales in excess of $3 billion. While I am not a huge fan of speculating about forward P/E ratios based on experimental drugs, Nuplazid's huge commercial potential, compared to Acadia's market cap, has this stock at the top of my watch list. 

Gilead Sciences is a no-brainer if prices continue to slide
Because of its record setting hepatitis C drug Sovaldi and its new teammate, Harvoni, Gilead should easily see its revenue double this year compared to 2013. And despite its share price climbing over 50% this year (it was higher before this pullback), industry experts have Gilead shares trading at a forward P/E ratio of a mere 10. While the likely approval of competing therapies may cut into Harvoni's commercial potential somewhat, Gilead also offers investors a handful of new HIV and cancer drugs to pick up any slack. In short, this stock looks like its only at the beginning of a long growth trajectory. Any further price dips would therefore make this stock a huge bargain, in my opinion.

Orphan drugmaker NPS Pharmaceuticals might have the highest upside
I am closely watching NPS Pharmaceuticals during this correction for two reasons. First, the upcoming target action date for the company's experimental long-term treatment of Hypoparathyroidism, Natpara, is close at hand (Oct. 24). Natpara's approval would give the company two commercially available orphan drugs, with Gattex for short bowel syndrome being the other.

These two drugs together are expected to generate about $500 million in peak sales for NPS. Although most orphan drugmakers trade at mind-boggling premiums, this scenario would have the stock trading at only five times peak sales at current levels. Moreover, this rough valuation doesn't factor in the company's other clinical prospects.

Secondly, Shire has reportedly been interested in buying NPS for some time, and may pursue a deal after AbbVie decided to reconsider its tender offer this week. Given Shire's history of buying orphan drugmakers and its desire to build out a rare disease portfolio, this is a deal that makes a lot of sense. The sticking point, to me, seems to be the massive premium NPS' board would likely want for the company. 

All told, I don't think NPS shares are an outstanding bargain right now, but my interest would be peaked if shares moved south with the broader market. 

Foolish wrap-up
The stock market hasn't crashed -- yet. So, I think it's a good idea to have a list of stocks to buy for the long-term in the event a crash does come to fruition. Because of their stellar growth potentials over the long-haul, I think Acadia, Gilead, and NPS are all worth a deeper look.