One thing I've found that has really helped is counseling. Even though i don't know what triggers the individual panic attacks, working through my other issues has helped decrease their frequency and intensity. My therapist also suggested that I cut caffeine and chocolate out of my diet. I couldn't give up chocolate, but I've been off caffeine for a year and a half now and it seems to be really helping- far fewer panic attacks, and nowhere near as intense. I do miss being able to order a Pepsi when we're out for dinner (no one keeps the caffeine free stuff on tap) but you know, I don;'t really need the extra calories anyway. And if I get to craving flavored coffee drinks, I've found most cafes have a few caffeine/coffee free versions of stuff.
Exercise also helps. Both during the panic and to help prevent it. Sometimes setting a goal- like, if I make it to X time (say, an hour, but you can use smaller increments if you have to- I've had to do 10-15 minutes before) then I can do Y thing (go to the hospital, call my therapist, take a pill etc) Or even just make myself focus on the small increment and forget about whats going to happen after (ie- I will walk for 15 minutes, then we'll reevaluate- which usually leads to another 15 minutes of doing something, then another. You cant stay panicked forever, its just not possible, even though it seems like it at the time.
Another thing I've found helpful is hypnosis/guided imagery. My therapist happens to also do hypnotherapy, so he makes me tapes to take home to help me relax when I start to feel panicky. Its nice because he can personalize it to me and what specific imagery helps me, but you could probably do ok with a generic relaxation CD too.
Actually, the first thing he does when I call him up panicked is make me focus on my breathing, which almost always calms me down- deep breathes in and out. I dont like it, and I dont know why it works, but its pretty hard for me to stay panicked if I'm focused on taking deep breathes in and out.
In the med/supplement department, if its really bad, I've been known to take a Unisom, which is just an antihistamine. I think they use two different ones depending on the formula you get. One, diphenhydramine, is the active ingredient in benadryl. The other, doxylammine succinate, is the antihistamine in Nyquil. I find the later works better for me personally, but I imagine it depends on the person. I would ask your doctor if you're needing to use it frequently, but as an occasional thing, its just an otc sleep aid, it shouldn't hurt.
I've also lately found that valerian helps calm me. I haven't tried a supplement per se, but have been using Celestial seasoning Sleepytime Extra Tea which has valerian in it. It doesn't make me sleepy, but it does seem to calm me down.
Other folks have good luck with Rescue Remedy. There are also some magnesium supplements marketed for anxiety.
