Northants have signed Scotland and Durham batsman Kyle Coetzer on a season's loan, while wicketkeeper Niall O'Brien has agreed a new two-year deal.
Meanwhile, seamer David Lucas, 32, will be released at the end of the season.
Coetzer, 27, recorded a knock of 122 against his new club earlier in the CB40 campaign.
O'Brien, 29, has excelled with the bat this year, averaging 48 in the County Championship and 52 in CB40, including a 121 against Hampshire in May.
"Hopefully I can help the club push on," he told the club website.
"I am looking forward to being part of the exciting things that are happening at Northants."
Head coach David Capel added: "I am pleased that Niall has committed himself to Northants once again and look forward to seeing him perform over the next two seasons, helping the club achieve our ambitions."
The Ireland international joined Northants from Kent in 2007 and has played 46 One-Day Internationals for his country, scoring over 1,000 runs.
Coetzer has scored over 2,300 first-class career runs, including five centuries and over 2,000 runs in the one-day game at an average of 34.
He said: "I'm looking forward to this loan and the opportunities it may bring. I hope to help Northants push for promotion."
Capel added: "I'm pleased that Kyle has decided to join us for the rest of the season, I see him as the kind of quality cricketer we want to add to our squad, and he will be able to join a team pushing for all important promotion in the County Championship Division One."
Lucas has spent the last five years at the County Ground, with his best campaign coming in 2009, when he took 60 wickets.
"The time has come to move on and explore other opportunities having been frustrated at the lack of first-team cricket this year," he said.