I think Introverted Boss is worth two tries - try from Episode 1 and then if you don't like it - try again from Episode 5 (I think that was after the re-writes?) with an open mind.
Lucky Romance has a nerdy and shy CEO/programmer with a more free-spirited, outgoing female programmer who sort of upends his world.
They're worth checking out to see if you like them but I'm not going to say either one is a "must watch".
'Ho Goo's Love' has a shy male lead, as does the brilliant 'In Time with You'. Oh and I forgot to mention, 'Sungkyunkwan Scandal' which has not one but two shy men/boys as well as another endearing male, leading to serious second or even third lead syndrome.
Ohitorisama the guy is generally insecure and shy depending on the situation. it's a "noona" romance, even though I shouldn't call it that when it's Japanese :p
