A lot of good recommendations have been made so far, but I gotta throw my heavily patina-ed two cents in and suggest the Bounty Hunter Land Ranger Pro. While I have not used many other machines or owned any others I continue to be surprised at the finds I have turned up in the 4 months that i have been detecting. While there is a stigma where Bounty Hunter machines are concerned, but what you get for the price with the Land Ranger Pro has impressed me so far! I also recently picked up a Teknetics 5in DD coil for trashy areas and have not been disappointed with that either!
That aside, don't discount considering a good used machine from a reputable source.