1. What are their benefits compared to your current benefits?  Health insurance, life insurance, relocation, working from home, vacation days (paid out vs. not paid out), commuter spending account, education reimbursement, parking costs, free meals, daycare, maternity leave, etc.

2.  Is there a bonus structure?  How does it compare to your current bonus structure if you have one?  Is it based on personal performance or company performance?  How often are you bonus eligible?  What percent of employees get the bonus?

3. What is the 401K plan?  Do they match up to a certain percentage?  Does this matching only begin after 1 year, 2 years, etc. or does matching start immediately?

4. Are there stock options offered?  Do these vest after 2 years, 5 years, or later? Would you rather substitute a cash signing bonus for these?  There's a lot of flexibility here for negotiating.

5. Will you be relocating?  If so, are the relocation costs 100% paid or are they only paid of you stay with the company for a certain time period (i.e. 1 to 2 years)?  If you leave before this time then they will make you pay back the relocation (it could be upwards of $20,000-30,000).   

6.  What non-monetary, experiential value will you gain from this position?  Will this job stretch you professionally and enhance your current skill set?  Consider the value of education and new skills.

7.  Do you gel with your prospective manager?  If they rub you the wrong way or are condescending to you in the interview, this job might not be a smart move.  You want to make sure the manager would invest in your success.  It's also important that you feel you can learn a lot from your prospective manager.  If you're not learning, you won't be satisfied. 

8.  What is the progression path for this position?  Is there one way up or are there multiple ways to grow with the company?  If the progression potential seems murky, you might be turning down a dead-end street.

9. How often is performance and salary evaluated?  Although they might say "quarterly evaluations," this might start after you've been with the company for 1 year.  OR they might evaluate each employee on their year anniversary, which requires them to evaluate a portion of the employees each quarter.  Read between the lines. 

11.  If you're moving to a new city, how will your cost of living change?  Use this calculator to make sure your salary reflects that change.  I like this one, Bankrate, and this one, BestPlaces.  

12. Check Glassdoor!  Look at a) employee reviews sorted by the date (newest to oldest) and b) the salary range for this position vs. the salary they're offering you.

13.  What is the company's reputation?  You have to protect your reputation.  Are there legal issues, unethical practices, or negative connotations associated with the company?  Or is it a company that is involved in giving back to the community, treating its employees well, and leading innovation?  As an employee you'll be a representative of your company, so you want to know 100% what you're representing.