Obviously, I'm not talking about a carry on. I'm going on a trip this summer. Can I make arrangements with the airline and have a rifle checked with baggage? Maybe a locked case, no ammo, etc.? I know it was possible in the past, but I have no idea after 9/11.

Yes, you can, but to stay out of a big hassle just call the airline your flying. I took two long guns on American last year. It was easier than I thought. The only requirment was to have them in a locked hard case and to sign a card stating that they were not loaded. This was in check baggage of coarse. I did get a lot of strange looks standing in the line with a gun case.

I thought I was going to have to fly with a shotgun on Southwest so I just askwed the attenddant on my departure flight about it. She said "not a problem". I told her I did not have a hard case and she said the only requirement is that the case (soft case) can be locked and then they owuld put it in a cardboard sleeve. I second the motion to just call and ask. Shouldn't be a problem.

Check your airline or potential others websites for their policies.  It seems that with TSA getting peripherally involved the rules have become more or less the same for all lines.  And the methods for checking in are publicized, before each clerk kinda made their own rules and hassled folks instead of learning what they should have known.  I carried a rifle a while back and it was straightfoward.

Thank you for the help and you guys were totally correct. But, I ended up not bringing my rifle. I  checked both Delta Airlines website, emailed them, and called. Each time I was told it is O.K., if you follow certain guidelines. I still decided not to risk it because of the Airport. I live in Miami (for only another month, moving back to Virginia) and was more worried about the airport giving me trouble. Miami is not the place to try and do anything out of the ordinary. I tried to call the airport itself and find out their rules, but I could never get anything more than a voice mail. I left several messages, but never got a return call. My wife and I were flying on a tight schedule and could not afford to be turned away. Now I know the rules and in the future, this will not be a problem.

Delta Airlines rules(quick+dirty version)
(1.) One firearm can be checked as baggage free of charge.
(2.) Must be in a hard locked case.
(3.) must declare that you have a firearm at every security stop.
(4.) rifle must be unloaded and you must fill out and sign a "unloaded firearm" form
(5.) up to 11 lbs. of ammo can be in the same case, but it must be in the original manufacturers boxes, no loaded magazines.
(6.) You can check more than one firearm, but at a additional charge.

That's basically it, to be honest I was more than a little surprised. I thought it was just "NO" after 9/11. These rules and guidelines are just for Delta Airlines, so I would check before you try it with another airline.

I've travelled with my AR and my Glock in March and April this year on United.

These are my tips I learned.  

1. Go to the inside check-in area.  Don't do it at the outside curbside check-they can't deal with the firearms.  Say to the the agent, "I'm declaring an unloaded firearm."  They'll ask to see the firearm briefly and have you sign/date one or two cards declaring the firearm is unloaded.  At one airport I was given two cards, one to place with the firearm, and one to hand to security when the xray the bag. At another airport, they put a reusable tag on the outside of the bag so the security screeners would know that its a firearm-pluss the tag inside.

2. Make sure all ammo is in an original factory type box.  Don't leave any in a magazine.  Makes it a pain if you CCW when you get to your destination, but they'll confiscate the ammo if you're lucky, otherwise a headache.  Boxed ammo only.

3. Get a hardsided case that can be placed inside another bag such as a duffle bag for a rifle or other suitcase.  This hides the fact that you have a firearm as your bag gets handled by the baggage guys.  I got a Cabelas all aluminum break down shotgun case for my AR.  It better conceals that it's a firearm and easily slips into a larger duffle bag.

4. I was asked to hand carry my own luggage to the additional screening area - CTX.  They will pass it through and depending on the amount of metal in your luggage or the scan of your bag, the CTX may prompt for an additional security check.  Stick around with your bag until it has gone through screening.

5. Lock the hardsided case with a heavy duty 4 number combo lock, in case you lose the key. If your bag is locked and you are around, they will ask you to either give them a key or combo.  You are also around to answer any questions they have about what you are carrying.  If your fiream is broken down and a cable lock through the action, the better it appears to the security guys that you are legit.  Know the weight of your ammo.  

6. By sticking around at the baggage screening area, you have the option to lock your baggage after its done screening.  Do this.  Ask for it.  Don't bring too much attention to yourself and firearm, otherwise the baggage guys that take your bags to the plane will have more information than they should know.  Only talk to the security folks about your firearm if they ask questions.  Some are very talkative and will talk about their own collections.  Others don't know what they are looking at and you'll have to wait until a supervisor comes over.  

7. Feel and act confident in what you are doing.  It will show to them that you are going by the book and know what to do.

I once had a loaded magazine with 10 rounds and forgot the empty factory box.  They had to call over a LEO to look at it.  They wouldn't let the mag to through loaded so I had to dispose of the ammo to the LEO.   I'll always remember my boxes now.

One time with the Glock and in a case inside another suitcase, the CTX didn't pick it out to be additionally screened.  My bag had that external tag declaring it was a firearm.  I had to grab the arm of the security guy and ask him to remove the tag, otherwise it just says Steal Me.

A funny add-on.  One time when I declared my firearm, I had to wait while agent got a lead agent and then had that agent track down "the form" to fill out.  I was wondering what was taking so long to get a little orange tag.  It turns out they thought I was a federal agent and gave me the form to carry my firearm on the plane.  I quickly corrected them and got the right form.  I didn't want any trouble, but think about what could have happened if a screw-up like this was on the wrong type of passenger.

-Doug