if you like Dredg, try Koma - Tsunami.
From postrock - definitely Mogwai, Godspeed You Black Emperor! (Slow Riot mcd would be a good start), Explosions In The Sky - The Earth Is Not A Cold Dead Place, Silver Mt.Zion..... Lanterna is also pretty cool, w/ dreamy atmosphere (Katatonia fans should check out the song B Minor from sophomore Elm Street)
From slow core - Isis, Pelican.... The Ocean are also kinda cool.
From 'shoegazing' pop or whatever, try Slowdive (every goddamn thing from them), Sigur Ros, or more rock-based The Loveless.
Wish you good hunt......