I hate to say it, but I think United will win it again. The main contenders will be them, us, and maybe Chelsea. I only say 'maybe' for Chelsea because I have doubts about Villas Boas, his age, and most importantly his lack of experience, I just don't think he is the right man for such a job, give him two, three years or so in the helm and I can see him having Chelsea right up alongside United and City, but not at the moment. Arsenal will do very well to get another 4th, anything beyond that for Arsenal should be considered a bonus. Could easily see either Arsenal or Chelsea dropping out of the top four.
As for Liverpool, to call them title contenders is going too far, I think some people have read a bit too much into what Kenny did last season. Look at the transfer business they have done so far, they have signed Henderson, who, in the grand scheme of things, didn't do that much last season and many would say is overrated, and Adam, who, even tough I rate him, is not Champions League quality. They are more than capable of getting 4th, maybe even 3rd, but not winning the league. Big season for Carroll, did he really do anything last season except score those 2 goals against us? I just can't see him doing the job required that would get Liverpool the title, he isn't quite that good.
As for relegation, I think Swansea really struggle, just don't think they are quite ready, equipped, or have the quality to do well in the Premiership. I think Wolves will also go down, and then the last spot will be between Norwich and Wigan.