where to start??
there are so many option open to you nowadays and it all depends on your expectations and budget, here is a small list of player types and web sites:
No-brand mp3/4 players:
these players are basic in quality and construction (generally) will usually have very little to no support and are made by one of hundreds of factories in china - i recommend the Rockchip based players with 2.4" color screens - DO NOT BUY NANO CLONE style players. these are cheap but work (most of the time) but will probably not last too long and dont expect any sort of comprehensive or sensible user manual
this iste has many players - i recommend looking at the 2.4" players which are usually rockchip based, the Temptation
looks quite sexy - many people on this forum have purchased from Uxcell with no probs
2. MP4nation - optimus range
this is mp4 nation basic (own brand) players, similar to uxcel above
these basic players come in a variety of memory sizes but average is 1mb to 2mb, but the advantage of many of them is that they will accept either mini sd cards or micro sd cards so you can expand the memory capacity as you need.
chinese branded players
These are becoming more and more popular and there are many to choose from. they use basically the same technology as the no-brands above but what you get is better build quality, official web sites and product firmware updates, many of them also have their own fan forums so support is nerver far away, some brands to look out for are:
many of the above players are based on the rockchip with some improvements made in functionality and sound oerformance. The Meizu stands out as it has been designed from the ground up, has superior build quality and excellent sound quality and its best feature is the catalogued music database allowing sorting of music by artist, genere, album etc - something not really found on thses style players - a lsit of stores below - i have purchased from all with no problems
House of dap
all these sites above offer a range of branded player from china and i have purchased form all of them at one point in time
of course you have all the big global brands to consider also. the advantages are obvious, global brand name, support, compatibility, quality are all the things you would expect, but you also pay a premium in price for this. i shal list a few but all you need to do is go to your local electronics store and you will find most of these
-- and the list goes on - i can not comment on any of these as i have never owned any.
it is up to you, may personal choice is a branded chinese player, my current best is Meizu M6 (excellent but not without small faults), i have a few rockchip based players for my kids and these work fine as they play movies, have games on and music too!!
this is all my own experience an opinion - hope it is of some use
cheers and good luck
ps - avoid ebay if possible but if you do, search this site first to see if the seller is on any black list - many mp4 sales on ebay are fraught with danger and may have had their fingers burned not to mention lost monay!!!