Situation 1: You don't make enough money. If the sole reason you want to quit is the money you're not making, consider the alternatives. Quitting over a lack of money is rarely the best decision. If there are other factors to consider, include those in the decision. But if it's all about the Benjamins, find another way to get what you want:
Ask for a raise. Research comparable positions at other companies on sites like Salary.com to see what you should be making. Assess whether you truly meet the background and experience requirements to make that much (be honest with yourself: if you could make $20K more but need a master's degree, you're not qualified for that big of an increase). If you do qualify, present it to your boss, along with a list of accomplishments you've achieved. You always want to back up your request for a raise with what you've done to deserve it.
Look for another position in the same company. If your position doesn't offer upward mobility, consider staying at your company in a different role. If there are no promotions opening up in your department, look at others, and check the intranet job board to see what's available. Tap your internal contacts to see where there may be an opening on the horizon.
Get a part-time job. If getting more money isn't an option at your current company, but you're still strapped for cash, consider getting a second job to provide more income. This way, you don't have to quit your job and you still earn additional income.
Situation 2: Your boss is verbally abusive. If your supervisor calls you ugly names and screams at you, it may be time to find another job. You shouldn't tolerate this kind of behavior, but understandably: you need your job. Still, the constant berating is likely wearing you down, and can even threaten your health, so in this situation, your best bet is likely to start looking for another position elsewhere as soon as possible.
Try to be calm when your boss attacks you, and don't feed the fire. Do your work and stay out of sight until you can resign.
Situation 3: You are dating a co-worker. Depending on what your workplace relationship policy is, you may be jeopardizing your job by getting involved with a co-worker. You might be fired if you're found out to be violating your company's policy ... or not. Sometimes companies have strict (seeming) policies in place, but they might be willing to turn a blind eye, especially if you're both hard-working and don't let your office romance interfere with your jobs.
Check with your employee handbook to see what it says about relationships. Then go to your human resources manager together and explain the situation. Get the HR recommendation on what to do. You may find you're able to keep your job and enjoy your new-found love.
Situation 4: You haven't been paid in weeks. If your company is late in paying you by several weeks and keeps promising you the "check is on the way," you should see red flags. This won't likely end well and you shouldn't have to suffer personally for the financial instability of your company. Insist on getting paid for the time you work and start looking for a new job.
Lindsay Olson is a founding partner and public relations recruiter with Paradigm Staffing and Hoojobs.com, a niche job board for public relations, communications, and social media jobs. She blogs at LindsayOlson.com, where she discusses recruiting and job search issues.