As much as I do not like Apple, the iPod is an exception. The reason it is so popular? It has decent to great sound quality for a DAP (depending on which model you buy), a massive amount of available accessories, it looks quite nice, is very user friendly, many different hardware/software modifications have been discovered for it, it has the best stock UI of any player out there, large capacities for cheap, comes in many different flavors (Classic, Touch, Nano, Shuffle, iPad, iPhone), is massively available and is easily found used or refurbished for very, very cheap. Beyond that, Apple has done a great job of marketing this thing.
For us, and especially the DIY crowd, I personally think that if you're a technologically inclined audiophile, the 5/5.5G iPod is probably one of the very best DAPs out there. There are so very many mods that you can do with this thing: iMod, DIYMod, WhipMod, iPodLinux, HDD upgrades, battery upgrades and Rockbox to name a few.
You can grab a refurbished 5G iPod for around 130 bucks with an extended battery pre-installed from RapidRepair. You can open it up and perform the DIYmod yourself (maybe $20 for parts at the most), install Rockbox and have an amazingly nice sounding DAP with FLAC capability for under 150 bucks.
If you want to go all out, you could install a 240GB dual platter hard drive for ridiculous storage capacity or a 64GB Compact Flash card and adapter for speedier performance while in use and better stability.
What's not to love at this point? It sounds great, it can be quicker or have a HUGE capacity depending on the hard drive replacement, gets great battery life, has tons of parts available if it breaks and after you install Rockbox, is easily managed with most media software.
