What is it you want to do?  
I looked at WMS, but with the costs for it and all the modules it just didn't seem worth pursuing.

WMS has its own GIS module that uses ESRI shapefiles.  I haven't been very deep into WMS yet, but we've just started using it for my Hydrology class so I'll get better with it in the next week or two.

I am basically trying to find out what stormwater software is on the market that can integrate with GIS.  In my limited searching, WMS seemed to be one of the bigger/better packages out there, but I really don't know for sure.

Ive also noticed that HEC-HMS has an add-on called HEC-GeoHMS that does some type of GIS integration. I do know know what features it employs or how easy it is to use.

I don't recall if SWMM 5.0 incorporates any GIS features.

I guess we are looking to utilize the wealth of information we currently have in our GIS databases. Automatic basin delineation, runoff estimation based on current land use categorizations, etc.

I wouldn't recommend HMS then.  The HEC-GeoHMS is only for ArcView 3.1-3.2 and it is a pain to use.  I have started using Arc 9.1 and it is so much better that I do not want to go back.  There is also a GIS add on for WinTR20 from the NRCS.  It seems less user unfriendly than GeoHMS.  It seems that there is a big difference in support of HMS compared to RAS which has really good GIS components that seem to get updated pretty readily.

Well, I'm a little more up-to-speed with WMS now, and I'm fairly impressed!  It has a GIS module (able to work with shapefiles) and hydrology modules that come with all the bells and whistles. I gather it's insanely expensive, however.

If you ask more specific questions I'll try to answer them for you.  (Well, in the next week or two, anyway as I'm done at the end of the semester and who knows when I'll do any hydrology again as I'm going off to work as a transportation planner... or maybe a design engineer; I haven't decided which of GIS and Microstation is the lesser of two evils.)

Thanks for the info. I've been busy and haven't had a chance to dive into the demo yet. I wish I had the benefit of a course to go along with the demo version; it appears to be fairly intricate upon initial inspection... and I have not been using GIS for very long either.