Toys R US (probably one of the cheapest places) Spreitenbach and Deitlikon.
Mac Baby - Altstetten http://www.macbaby.ch/content/index.php
Baby Haus - Jona - http://www.kaenguruh.ch/ Best prices I found for trip-trap and Romer car seats.
There's a big baby place opposite Hornbach in Littau (but never tried it).

As mentioned before H&M has clothing, also Manor etc...

Try a few google and/or telephone directory searches too.