I'm very excited because I purchased a buffalo linkstation pro (LS-500GL) which I've been waiting for a very long time(actually any linkstation but this one was on sale). I purchased the linkstation mini 1terabyte for $237 from frys a few weeks ago but frys.com argued it was a price mistake; broke my heart. I am a huge fan of products that are hackable aka have their source code opened up so you can use their products beyond their lifecycle. This is important because for example I have over 5 netgear routers that are absolutely useless that I still have but havn't used(5 years now) because they suck and cannot be improved. Whereas my Linksys wrt54gs v2 is simply incredible. However since linksys has started to eliminate their routers(lower ram/proprietary) except for the wrt54gl; I too have pretty much avoided their products. Here's a list of my favorites
1)Linksys NSLU2 - My favorite usb nas device with 8MB Flash/32MB Ram. This will probably be the only Linksys device I will buy from until they discontinue it. I particular like using flash drives and setup small servers like music/ftp/files because I leave them on 24/7 at 5Watts is great(I have 3 on 24/7). I tried to setup a video media server like twonkyvision, openshowcenter, slimserver, swisscenter, oxybox, etc but unfortunately the use of apache was too much on the nslu2 (out of memory, crashing) and lighttpd didn't seem to be able to serve the video files well for me.
2)Asus WL-500g Premium v1 - 8mb flash/32mb ram but with usb output. This became my favorite router after linksys started making newer wrt54gs with less ram/functions. Unfortunately Asus went the route of Linksys and made version 2 which does not work so well with openwrt. DD-wrt is available but it didn't feel the same anymore. I used this as a wireless usb printer and hosted some other services. Version 2 of the wl-500g premium is still good and worth investing as primary router.
3)Buffalo Linkstations - These are my favorite media devices. I was operating a video media server from my mac mini because of electric costs but with linkstation it would costs less than half what I was paying. The linkstation operates only around 20 watts but only models LS-GL or HS-DHGL because they have a high cpu speed of 400mhz and 128MB Ram. Kurobox Pro(also made from buffalo) is an alternative but they are never on sale.
*- Asus EEE PCs - not exactly open source but because they are extremely low powered if you do not attach the battery and have sufficient memory/cpu/hard disk they make exceptional apache/mysql web servers. You simply cannot do this on the other open source nas appliances with limited memory and processor power to handle a large number of users with dynamic data. They also are very versatile. Go with the low cost options but opt for SSD hard drive, Linux OS but most important; best CPU processor and Ram can be upgraded to 2gb.
Can't think of anything else except for a mac mini which is incredibly decent as a powerful server with very low power requirements that you must buy but if you see them on sale; Do not hesitate to BUY!