This came up as a problem for me last year, when Icelandair (FI) substantially reduced service from MSP and I had to fly to BOS to connect to my FI flight.
I learned this, and I believe it is still true. Any airline that is a member of the International Air Transport Association (IATA) must, as a requiremembership of membership, accept baggage for interline transfer to any other IATA carrier.
Before I did my research, I thought almost all airlines are IATA member airlines. Not so.
Here in SEA, as strange as it might seem, Air Tran, Frontier, Jet Blue, Midwest, Southwest, Sun Country, and Virgin Air are not.
In my own case, I had purchased seperate tickets (SEA-BOS on AS, and BOS-KEF on FI) and it was no problem to check my bag at the counter in SEA all the way through. The agent just needed to see my ticket documentation printout from FI. Worked great.
You can see a list of IATA airlines here:
http://www.iata.org/membership/airli..._list?All=true
If you look at this list, you can see that QX is not IATA, so I'm not sure what would happen if you were on them as opposed to mainline AS.
So, to answer your question, Alaska, by being a member of IATA, has interline baggage agreements with all IATA carriers. But there may be other carriers, if a special agreement is in place. You would have to call Alaska about that.
Is there a specific carrier you were looking for?