Most investors don't keep tabs on their companies' fundamental value. That's a mistake. If you take the time to read past the headlines and crack a filing now and then, you're in a much better position to spot potential trouble early. Better yet, you'll improve your odds of finding the underappreciated home run stocks that provide the market's best returns.

We can help you keep tabs on your companies with, our free, personalized stock tracking service. Here are five stocks from my watchlist:

1. Cell Therapeutics (Nasdaq: CTIC)
A year ago, the Food and Drug Administration rejected Cell Therapeutics' application for its drug Pixuvir as a treatment for non-Hodgkin's lymphoma. The FDA was concerned that trials did not show the effectiveness of the drug, and the agency asked the developer to conduct another clinical trial. Cell Therapeutics appealed the decision and is awaiting a ruling on its appeal during the first quarter of 2011. There has been some good news, however. In mid-March, the firm announced it would be working with Chroma Therapeutics to develop its cancer therapy tosedostat. The drug, which is similar to Celgene's (Nasdaq: CELG) Revlimid in that it is a tumor selective targeted therapy, is in the late stages of testing and if approved would be a boon for Cell Therapeutics. Definitely one to watch.

2. Avanir Pharmaceuticals (Nasdaq: AVNR)
At the end of October, the company's shares doubled when the FDA approved Nuedexta, the firm's treatment for pseudobulbar affect, or PBA. Neudexta has no competition right now as it is the only drug approved to treat PBA. This provides a big opportunity, though not huge, and analysts estimate the drug could attain as much as $500 million annually in sales. However, that would be a huge deal for Avanir, which over the past 12 months had only $3 million in sales. The company is a good candidate for a buyout from a big pharmaceutical looking to build out its portfolio, and it is definitely one to watch.

3. Sunesis Pharmaceuticals (Nasdaq: SNSS)
Sunesis is developing vosaroxin, a leukemia drug in late stage trials. If approved, it would be a huge win for Sunesis as there is barely any competition in the acute myeloid leukemia market. As CAPS member akshara3000 wrote in January, "If phase 3 trial info is released midterm through the study, and it is as positive and consistent as previous results, the stock will jump remarkably, especially after being beaten down so badly since mid 2010."

4. MELA Sciences (Nasdaq: MELA)
MELA Sciences built the MelaFind handheld scanner, a device for identifying skin lesions for cancer-testing biopsies. MELA is a risky stock, having proverbially died before when the FDA released briefing documents expressing a negative opinion to an advisory panel in November. However, the advisory panel voted 8-7 that the benefits of MelaFind outweighed the risks, causing the stock to surge 95% in one day. MELA has since given back those gains as it waits for the FDA's final ruling. Should the FDA approve the device, MELA will skyrocket. Until that time, though, I am watching MELA Sciences -- and you should, too.

5. XOMA (Nasdaq: XOMA)
Last month XOMA's self-titled XOMA 052 drug failed a phase 2 trial for diabetes, causing the stock to plunge. Luckily, XOMA 052 also has potential to be useful for those who suffer from cardiovascular diseases. Currently trading slightly higher than the $60 million of current assets on its books, XOMA has a long road ahead of it testing the drug, but it should have enough cash to make it happen.

Bonus! 6. MannKind (Nasdaq: MNKD)
Always give more than expected. That's what I'm hoping for from MannKind, which has the potential to revolutionize the insulin industry with its inhaled insulin product. The company is grinding to survive, announcing in February that it was cutting 40% of its staff as it waits to complete two clinical trials required for FDA approval. If successful, inhaled insulin would be a leap above injecting insulin, changing the lives of thousands of diabetics who would no longer have to carry around potentially hazardous needles with them at all times. CEO Alfred Mann certainly believes in the company and has been buying shares for his own account. Certainly one to watch.

Foolish bottom line
If you're looking to keep up with these companies, add them to your watchlist. If you're looking for some full stock picks, the Fool recently wrote a report highlighting five stocks that Motley Fool has bought for its own account including the stock that senior writer Morgan Housel calls "probably the world's greatest investment." If you'd like to see the entire buy thesis on that stock, as well as the other four, I invite you to download it for free. Just click here.