New Server build, need hardware suggestions

Hello everyone!

Current I have a home server and a separate NAS that I'm looking to combine into one, plus give my server a little more power for what its used for so I'm looking for some hardware suggestions. The NAS is from Snology and is used only for storage.

Current Server:
[CPU] Intel Core 2 Quad @ 2.4GHz
[MB] Some Asus Motherboard
[RAM] DDR2 4GB of Kingston Ram
[HDD] 2x 500GB 7200RPM HDD Raided for redundancy
[PSU] CoolerMaster 500W

I'm looking to use the server for the following:

- LAMP
-- WordPress Sites
-- Mobile Web Services

- TeamSpeak 3 Server

- Postfix Mail Server

- Downloading
-- NZBs
--- SABnzbd, Sickbeard, Newznab (Indexer)

- Network Media Streaming to a HTPC
-- 720p and 1080p Content

- Web Development

- File Server
-- Desktop Backups
-- FTP

- VPN End Point

The big hit on performance is the NZB downloading as SABnzbd (Downloader) will auto repair and extract archives once they have completed downloading so this takes up a lot of CPU and RAM (if I'm processing more then 2-3 HD content my RAM usage can reach 80-90% just for SABnzbd), as well as WordPress depending on site load can use a good amount of resources as well.

So I'm looking for Intel hardware that will do the above without a sweat but I'm not looking to spend anymore then around $600, no video card is required as it will be a headless Ubuntu System; integrated GFXs is a plus but not required. And I don't require hard drives as I will recycle them from my current server and NAS. I do require a PSU as my current server will be going to my Mothers as her desktop.

Thanks