The danger, of course, is in fanciness and formality. But just because the prayers are formal doesn't mean they must lack sincerity. They actually provide a wonderful means of allowing the mind and heart to engage in seeking God. We just need to make sure we use them to that end.
Here is one we used a couple weeks ago during services at Oxford Bible Fellowship:
(adapted from The Valley of Vision, p. 78-79)
God of all grace, You have given me a Savior, produce in me a faith to live by him, to make him all my desire, all my hope, all my glory.
May I enter him as my refuge, build on him as my foundation, walk in him as my way, follow him as my guide, conform to him as my example, receive his instruction as my prophet, rely on his intercession as my high priest, obey him as my king.
May I never be ashamed of him or his words, but joyfully bear his reproach, never displease him by unholy or imprudent conduct, never become proud if I take it patiently when disciplined for a fault, never make the multitude my model, never delay when your Word invites me to advance.
May your dear Son preserve me from this present evil world, so that its smiles never allure, nor its frowns terrify, nor its vices defile, nor its errors delude me. May I feel that I am a stranger and pilgrim on earth, declaring plainly that I seek a better country, my home in it becoming daily more clear, my fitness for it more perfect, my foretaste of it more abundant; and whatever I do, may it be done in the Savior’s name. Amen.
Check out more Puritan prayers at these websites:
Tim Keller post on a similar theme.