Here is what I would do. If my time horizon was beyond 10 years, I would be as aggressive as possible. This means a lifecycle/target date fund (owning index funds) with the biggest number attached to it. The other option would be to select some combination of a small-cap, international, and large-cap mix, preferably broadly diversified index funds.
Once I came up with a plan, I would sock that money away each month and ignore everyone who tries to predict the market. If I got matching money in individual stock, I would monitor it carefully and sell it one time each year, and then move the money into the funds that I just mentioned. Keeping much, if any, money in your company stock is unwise. Read about Enron, Tyco, and Lehman for further details.
If you are young, you will probably have many employers over your career. Every time you start with a new employer, review their retirement plan carefully and start investing immediately. Find out how long it takes to get vested (the time it takes before that matching money they give you is YOURS). This is usually around 5 or 6 years.
When you leave an employer, take your plan with you. This is quite simple. Go to vanguard.com and have them transfer your money (you want to do this trustee-to-trustee, without touching it yourself to avoid any possible penalties or taxes) into a traditional IRA (from a traditional 401K) or a Roth IRA (from a Roth 401K). DO NOT let your retirement accounts languish at previous locations. Go get it!