For example, Windows talks with the 3Ware card as if it were a hard drive, and the 3Ware card takes care of writing content to the raid as an asynchronous process. This frees up the CPU from disk operations.
Including 3Ware, what Server raid cards should I consider that truly separate raid operations from the server? Contrary to popular believe, it's very hard to find cards that actually do this similar to 3ware.
Not sure it's hard at all, look at Adaptec, HP, IBM, Dell, Sun and LSI to name a few, they all make purely hardware driven disk controllers.
pretty much any hardware raid card that has a BBU option. Try LSI, Adaptec, most Dell PERC, Intel, HP, etc.