Out-of-contract pair Tommy Miller and Shefki Kuqi have left the club. Miller will sign a two-year deal with Sunderland, while Kuqi looks set to join Blackburn Rovers.
Boss Joe Royle announced the news to the club website: "I can confirm that both Tommy and Shefki has chosen to look elsewhere for their football next season.
"We made excellent offers to both players, as good as we could make at Championship level, but the lure of the Premiership has proven too great.
"I'm sorry to see them go and wish them every success in their future careers, but now I know where we stand for next season and can start looking ahead.
"It's been a waiting game for us to see what decision the out-of-contract players made, but we have had plans in place for a while and will now step them up to bring in new recruits.
"We are talking to a number of players and things are moving along but it's not a race. There's still plenty of time to get the squad I want in place before the start of the season - a squad that will challenge for a place in the Premiership."
Miller had interested Leeds, Crystal Palace and Celtic, while the Blues had offered the former Hartlepool man a new two-year deal. However, the attraction of moving to his local club always seemed likely to prove too tempting.
The 26-year-old rejoined the Blues in the summer of 2001 for £800,000, having been released by Town as a schoolboy.
Miller made 139 appearances while at Portman Road and scored 36 goals.
Kuqi signed initially on loan from Sheffield Wednesday in September 2003 and joined permanently on a free transfer two months later.
The Finnish international made 88 appearances for the Blues, scoring 35 goals, and was the winner of last season's Player of the Year award.