With regards to Portishead, I am not sure if they are releasing any new material, but Beth Gibbons just released a solo album with 'Rustin Man', who apparently was involved with Talk Talk at some point. It's gettting some pretty good comments from various avenues and is undoubtedly a very nice recording. It is, unfortunately, only a fairly expensive ($20+) import at the moment, unless you happen to live in the UK I suppose.
P.S. Speaking of Talk Talk, anyone who has written them off as an '80's pop band should check out their later material, particularly 'Laughing Stock'. Very interesting and adventurous jazz/post-rock hybrid music that stands in a musical realm of it's own. Surprised the heck out of me anyway...