Xeon E3 = Low end Workstations and Server, Single Socket only, based on consumer platforms like LGA 1155 or 1150. You can basically say that they're pretty much identical to mainstream Core i5s and i7s with some extra features aimed to the Workstation and Server market like ECC Memory support.
This like had the Xeon E3 with no V on them (Sandy Bridge), Xeon E3 V2 (Ivy Bridge) and currently Xeon E3 V3 (Haswell).
Xeon E5 = General enterprise platform, that can scale up to 4-way multiprocessor systems. There are two things that you have to watch for: First, that there are TWO totally different Sockets for current Xeons E5, one that uses a pinout amount similar to Nehalem. LGA 1356, that only allows for Dual Processors and Triple Channel, and the other that is LGA 2011 (Like high end Core i7s) that allows for Quad Processors, Quad Channel and has all the goodies. The first one is the Xeon E5 x4xx line, while the full fledged ones are from the E5 x6xx line. You also pay a price premium for how many total Processors your system is going to have (They should be otherwise identical). Xeons E5 4xxx are intended for Quad Processors, E5 2xxx for Dual, 1xxx for Single like LGA 2011 Core i7s.
This line includes Xeons E5 1400 and 2400 for LGA 1356 with 1-way or up to 2-way, and Xeons E5 1600, 2600 and 4600 for LGA 2011. You also have Sandy Bridge-E versions that don't have a V, and Ivy Bridge-E versions that have a V2 on them. Ivy Bridge-E was released months after Haswell, so you had Xeons E3 V3 yet Xeons E5 V2 weren't even released. Xeons E5 V3 will be Haswell-E based and will use a different version of LGA 2011 incompatible with the current one for SB-E and IB-E.
Xeons E7 = High end enterprise, mission critical with tons of RAS support, up to 8-way. The most badass models got 15 Cores (Xeons E5 top at 12).
You have older Xeons E7 based on Nehalem that uses a different nomenclature, the current models that follows the other lines nomenclature are all Xeons E7 V2. They're all Ivy Bridge-EX (Which was released after IB-E), as they skipped the Sandy Bridge generation for these. Oh, and they use yet another different and incompatible version of LGA 2011.
If you want a Single Socket Xeon Haswell with DDR4 support, you should wait until Haswell-E gets released and grab a Xeon E5 1600V3 with a LGA 2011 Motherboard intended for those.