The number ONE best piece of advice I can give for separation anxiety is:
Be nonchalant & have a pattern/routine.
If you're choking up, afraid, or nervous...they get that. Kids are wired to look to us to see what our reaction is in any given circumstance...and to echo that. If we're reacting with nervousness/stress/tension, they get that. If we're business as usual...they get that too.
Patterns (like at bedtime) are reassuring. If you do the same thing every time you leave, it imprints on them..."She does that, she leaves, she comes back, she loves me".
For US, our pattern was after hugs and kisses goodbye, I would wave all the way to my car, and then wave out the sunroof...alternating with blowing kisses like a movie star. I did it at preschool, daycare, when I was going to the STORE for 5 minutes. Whenever I left I waved in a REALLY overblown matter. I know others who beep a horn, or keep the ritual totally indoors, or do a high five, but whatever the ritual is, they do it every time.
2) If your daycare is giving you issues, look into changing daycare. My personal, unbendable rule for daycare/preschool/school, is that they have to be Safe, Fun, & Interesting. Our daycare provider (nanny-type) met that, our preschool met that (we had to look at nearly 50, and only THREE met those requirements), and NONE of the public schools and only two of the private schools in driving distance met that. Daaaang. What does it take??? C'mon, people!!! My point here...is that it can be hard to find a place that meets or exceeds your own expectations...and meeting those expectations is IMPORTANT. Just because it might be a "good" place, or is beloved by "x" other people, doesn't mean that it's the right place for you or YOUR child.
3) Our son had FANTASTIC care, and still would do the separation anxiety thing once or twice a year. One thing that I loved about our preschool is that one of those "bouts" was "solved" by not sending him in the 3 days in a row that they "require"...montessori. Instead, he went Monday, Wed, Thur. Our son was flipping out on Tuesdays (I worked a 15 on Mondays at the time and was gone all that day). We switched it, so he had tuesdays with me -i had that day off anyway...it was just the school requirement that had him in school that day anyway-, and boom. Problem evaporated. The next year, he did tuesdays no problem, with no problem at all. It just took him awhile to adjust to my "gone on mondays" schedule. Gosh, I LOVE that preschool. Their attitude, was "whatever works best for your family".
Other times...we just had to smile and laugh and hug and ride it out. It would usually last around two weeks at most. Sometimes it was severe, sometimes it wasn't. But it was thankfully, always short. I think a lot of it was that the hug-kiss-normal-business approach worked so well with his personality.
We went with that approach on advice from my mum, who's opinion on these bouts of anxiety is that there's been another cognitive leap...and no matter how much they KNOW you've always come back, what if you don't THIS time? Reassure them through it, hugs, kisses, laughter, and waves goodbye...and remind them "See? I always come back for you!" with hugs and kisses whenever I picked him up.
In any event...that's what's worked for US. We all find our own balance.
:) Z