Separation Anxiety and New babysitter/daycare

DS is 18 months and has pronounced separation anxiety.  If we go to storytime or a music class, he clings to me.  When I try to drop him off at the Y daycare, he goes into hysterics, and I have to come get him.  A few weeks ago, I dropped him off at a friend's house for a playdate for 1.5 hours, and when I went to pick him up, he was crying uncontrollably and they weren't able to calm him down.  He has been going to the same daycare since he was 5 months old, and he loves it there, and I don't have any problem dropping him off for daycare, thank god! 

Our daycare closes for spring break next week, and because I get so little time off, I've arranged for him to go to another sitter's house where there will be two other kids about his age.  We visited the sitter this weekend, and once again he clung to me.  I'm really dreading the drop off next Monday morning because I know he will be in hysterics when I leave, and I really could see him crying for an extended period of time.  I'm not sure what I'm looking for here - maybe just reassurance that he won't cry all day long.  Or advice on things to do to help ease his transition (we'll bring whatever his favorite toy seems to be next week and his Elmo doll and I'll let him have his pacifier whenever he wants it).

Thanks!