Here's a standard opening that many people have used in the past:
I am seeking new challenges in my career. The Dishwasher position at XYZ Company is of great interest to me and I know I will be a great fit.These days that is the bare minimum requirement for an oppening paragraph. In today's business world if you're breathing you should be seeking new challenges. Instead of that tired and boring opening, this is where you should be using your ability of wordcraft to show you're right for the job.
The opening paragraph should also include the exact job title as listed in the want ad, how you heard about the position, and any personal references you have (ie, "Joe Dobson of the sales department and I have discussed the Sales Manager position and he has been kind enough to pass along my resume to you, I can't thank him enough for the opportunity." or "I am sending you my resume after researching the position of Sales Manager that XYZ Company had listed on Monster.com.")