I'm looking at the various transparent caching solutions available as per Cisco's Cache Engine.

Can anyone tell me of any other products that work in a similar (transparent) manner and any experiences with these ?

We make one called the Web Gateway Interceptor, which we distribute through the fine folks at <URL:http://www.mirror-image.com/>. A handful of folks on the NANOG list have tried it or are running it now, with varying degrees of success. Network Appliance's <URL:http://www.netcache.com/> is planned to be offer transparency at some point but I'm not sure whether the high-performance cache box (based loosely on their NFS server appliance) they're shipping actually has transparency right now or not. NetCache is Peter Danzig's "Commercial Harvest" by a new name. Peter works for NetApp now. Inktomi <URL:http://www.inktomi.com> has announced their intention to offer transparency but they are not an appliance (like Cisco, Vixie, and NetApp) and last I heard they were waiting on some Solaris kernel changes before they could actually ship transparency. Transparency turns out to be really, really hard from an HTTP level. When you're a transparent cache none of the normal HTTP rules apply to you -- or sometimes more than one conflicting rule applies to you. At times you are a client, at other times you are an origin server, and rarely, you are a proxy. We've had to use our customers' log files and complaints over the last year or so to figure out a set of rules which minimize complaints. At the moment they also tend to minimize hit rates compared to our earlier product, but we're working on that. One thing to note about caching in general is that the page splay is too wide for any single cache to do you much good. Multilevel caching, in the style of the ICP projects such as Harvest and NLANR, is the only way to get reason- able (reasonable means "50% or higher") cache hit rates in real production. Multilevel caching depends on moderate sized primary caches (~10GB) sharing access to a larger (~500GB) secondary cache. A single primary cache (say for example, a transparent cache in front of 1000 modems) won't see enough query duplication before purge rollover to make its hit rate really interesting.