Swiss trains.

There are lockers in the larger stations, but not in the smaller ones. I can't find a list of exactly which stations, but if you click here: http://www.sbb.ch/en/station-services/am-bahnhof/railway-stations.html you get a list of the largest stations and the facilities there.

Information and prices on sending luggage ahead is here: http://www.sbb.ch/en/station-services/services/luggage-and-flight-luggage/luggage-product-comparison/luggage.html
The basic price is CHF 12 per item. This can only be done to and from manned stations (of which there are about 400).

You can find information about any station here: http://www.sbb.ch/en/station-services/am-bahnhof/railway-stations/bahnhof-finden.html
You can for example enter Wengen and it says: Luggage pick-up Mo–Su 07:00 – 20:00

When looking up train times and other details for a station be aware there are many stations in Zürich, and you need to enter the name of the one you want. The main ones are Zürich HB (the central station in the city centre) and Zürich Flughafen (the airport).

There are lockers in the larger stations, but not in the smaller ones.

My experience is that most all stations big or small have lockers...especially in touristy areas.
You can search for lockers via this link:
http://tinyurl.com/nmwyx3v

Lockers will be listed under the "equipment" tab. Be aware that Swiss Rail's info isn't complete. There are some stations that do have lockers which are not listed like the Interlaken West station.

We used the medium/large lockers at Zurich station during our daytour and they worked out just fine. There were several locations on different levels, the change machine at ours was busted so I just walked over the another area and used theirs.

Are the lockers large enough for skis?