www.flashpanoramas.com is the trendy choice, gives instructions to manually create your pages. requires flash 9
immervision is probably the cheapest, buy the basic package get the flash viewer included. requires flash 9
pano2qtvr is a bit pricier but includes quicktime creation and works with flash 8 which makes it more compatible but a little shakier.
All in all most people go with flashpanoramas.com but I rather like the look at immervision's which strikes me as a little smoother scrolling. They both have a quite nice update your flash plugin system for customers who are not up to date.
Probably better to try browsing their forums at http://www.immervision.com/forum/ as while I have fiddled around with their free java version I haven't tried the paid for stuff yet or the flash.
I think though the splasher only works with their java viewer so your stuck with with flash one. You can download the documentation for the flash viewer without buying it so have a browse through it and see if it looks like it would be suited for you. None of the immervision stuff is very automated and tends to require fiddling around with the html and stuff youself.
Personally I would go with Pano2QTVR (Flashpack) software and create a real .swf file. There is much better value in this software when compared with Immervision version. (Yes, I have both)
Pano2QTVR (Flashpack) allow's your own splash screen.