What is a good slide phone for at&t or Tmobile?

I currently have a sony ericsson W550i and i'm thinking of buying a replacement so what should i get and is there a place where i can just buy a phone with out a 2 year contract an stuff so i can just put my sim card in the new one

You can only put your sim card in a phone sold by the company you use. I used to have the Samsung a737 (i think thats what its called).. and its a nice phone. On ATT there's also the Matrix, Propel, and a lot more if you go to their website. When you click shop all phones, on the left you can narrow your search down, just check off the box that says slider phones.