PLEASE READ FIRST

wanted to name exactly those games as well.
as for portal: in a less direct-copy way you could merely enable the main character/element to "zoom" to another position, while things around remain "frozen". would make for a great many timing-based puzzles.
Another variant to look at, while not exactly the same way, is the flashgame "Shift" + Sequels. Basically it introduces a dimension switch(together with gravity gameplay), meaning there's usually two variants of every level, despite them being identical(hard to describe, but easy to understand if you just play a few levels).

Gateways - I forgot about it, thanks!
Also thanks for so many games, will check them definately! :)