I think the classic looking readers are very easy to read.
Penguin Magic Marked Cards - These cards are said to be, and I quote, "The most clearly marked deck in the world". I'm not sure, but I believe they are just marked - not readers.
They are marked in 6 different spots on the cards. They only cost $10 per individual deck and only
$5 per deck in a brick. Clearly the most cost effective if you buy a brick.
Ellusionist Marked Vintage 1800s deck - A reader deck with relatively easy to read markings. Essentially your rider backs, with an old look to them, but only
$7.49 per deck - Most cost effective for one deck.
GT Speedreader - These are Readers (from what I understand) printed on the classic Mandolin Back. Super easy to read. They also have their markings in better positions then the standard places. Cost $19 - $25 - starting to hit the pricey side.
TXI's The Code by Andy Nyman - From what I have been told, this is a stunningly simple reader deck that has its markings well hidden. It costs $29.95, but comes with a full DVD set with many tricks.
The Ultimate Marked Deck - A reader on the exact Rider Back design we're all used to. Markings are easy to read and well hidden. Costs $29.95 as well.