More details before I could suggest someone....
Are you a large corporate client that can afford $10k+ per month for SEO?
Are you a small website where a $100 a month for SEO is more your speed?
Obviously the large SEO firms don't want the second guy, and the firm that services the 2nd guy is probably only dreaming about finding the first.
There are also mid-size firms that hit the middle of these two. It also depends somewhat on what vertical you are in, how competitive it is, and precisely 2.4 million other variables.
About the only thing I would not suggest is Google'ing SEO and then clicking on a paid ad... That is likely to not end well.
Might also consider sending a PM to SEO_Mike he does SEO for a living and is probably looking for a few new clients at the moment.