Demokritos would be proud: if you look very closely, you'll see that Omniture's "SiteSearch" offering is actually composed of Atomz -- one of the original players in hosted site search. The products we cover my be acquired, renamed, or folded into another product, but they seldomly really disappear without a trace.
The path of this particular search solution has certainly twisted around the mountains a few times. In 1999, Atomz launched its hosted offering, which became a popular way to add a search box to a website (there was a free and a paid version). Then, in 2005, Atomz was acquired by WebSideStory. WebSideStory acquired Visual Sciences in 2006, and in 2007, the whole company renamed itself to Visual Sciences. Shortly after, the company was bought by Omniture.
What happened to Atomz Site Search through all of this? Well, surprise... it's still there. You can still sign up for free (ad-supported), or paid search (add-free from $80 to $250, based on the number of documents). And the atomz.com domain is still registered to WebSideStory. Though of course, it is now owned by Omniture.
Omniture SiteSearch, however, is not quite the same thing as the free Atomz service. That's not to say it's entirely different -- at launch, the product already boasted a surprisingly large number of large customers, but if you look closely, many of their search results are still served from the Atomz domain.
On the plus side, if you subscribe to Omniture's hosted search, you get the possibility to have site analytics (from SiteCatalyst, of course) actively influence search result ranking. That can be a powerful add-on for, say, e-commerce purposes.
So, Atomz is still a pretty basic website search solution (comparable to Google Custom Search), and Omniture SiteSearch consists mostly of Atomz. Yet, it now has one extra tab in its interface for the analytics based ranking, however, and that moves SiteSearch from basic website search to the e-commerce arena. There, it competes with Endeca, Microsoft's recently announced Fast for Internet Business, and Autonomy's new e-commerce features.
For that reason, we've added a new evaluation of Omniture SiteSearch to our Search & Information Access Report 2009, where you can find many more details about the service. Meanwhile, if you're looking for e-commerce or website search, you may find that there's quite a few options out there. All of them are quite capable, but have very specific strengths. Finding out which one is suited to you, and your specific scenario, might pay off.