"Well, Unity is not only a beautiful place as we can see, it's a wonderful feeling isn't it?" Clinton said, standing beside Obama before 4,000 people.
"And I know when we start here in this field in Unity, we'll end on the steps of the Capitol when Barack Obama takes the oath of office as our next president."
Clinton addressed any of her backers who are considering voting for Sen. John McCain, R-Ariz.,: "I strongly urge you to reconsider."
Of Obama, she said, "I know that he'll work for you. He'll fight for you, and he'll stand up for you every single day in the White House," Clinton said, calling Obama "a leader who invests in our future."
When it was his turn at the podium, Obama praised his former rival's dedication and tenacity.
"For 16 months, Senator Clinton and I have shared the stage as rivals for the nomination, but today I could not be happier and more honored and more moved that we're sharing this stage as allies to bring about the fundamental changes that this country so desperately needs," Obama said.
"Hillary and I may have started with separate goals in this campaign, but we made history together," he said. "I've admired her as a leader, I've learned from her as a candidate. She rocks. She rocks. That's the point I'm trying to make," Obama said as the crowd cheered.
In a further gesture, Clinton, who is still heavily in debt for her own presidential bid, made a personal donation to the Obama campaign Friday. She and her husband, former President Bill Clinton, maxed out to Obama online giving $2,300 apiece.
Obama has also hired Neera Tanden, former Clinton campaign policy director, to be his domestic policy director.
Obama and Clinton wore matching colors for their first joint appearance together -- he a white shirt and baby blue tie, and her a pantsuit of the same color.
During the rally, members of the crowd chanted: "Thank you Hillary!" and one member of the crowd held a homemade sign that said "Obama/Hillary Unite!" and "Hillary for VP."
Clinton, Obama Urge Focus on November
Obama and Clinton sat beside each other on his campaign plane in view of reporters who accompanied them on the flight from Washington DC to the Granite State.
The once-rivals spent Thursday evening at the Mayflower hotel in Washington, D.C. showcasing that unity for a group of top-dollar Clinton fundraisers.
Obama tried to win them over by personally writing a check as his contribution to paying down Clinton's $10 million campaign debt.
Inside the room of 300 or so moneymen and women, Obama and Clinton urged the gathered group to move past a divided primary season and to focus energies on the race to November.
Warm Reception, but Tensions Remain
The former rivals said winning the White House was paramount. The mood inside was strained but supportive.
"This was a hard-fought campaign. That's what made it so exciting and intense and why people's passions ran so high on both sides. I know my supporters have extremely strong feelings and I know Barack's do as well," Clinton said. "But we are a family and we have an opportunity now to really demonstrate clearly we do know what's at stake, and we will do whatever it takes to win back this White House."
Obama complimented Clinton on a hard-fought race acknowledging loyalties remained and harmony might not come easy.
"I recognize that this room shared the same passion that a roomful of my supporters would show. I do not expect that passion to be transferred. Senator Clinton is unique, and your relationships with her are unique."
But he added, "Senator Clinton and I at our core agree deeply that this country needs to change."
Clinton and Obama were warmly received by the crowd, but several attendees said they couldn't help but feel tension, even while they were likely to play supportive roles in Obama's race against presumptive Republican nominee Sen. John McCain of Arizona.
One major Clinton donor described it as an uncomfortable family visit.
"This felt like when your mom forces you to go visit your Aunt Ida and she has to pinch your cheeks and you're sitting there in an uncomfortable suit and you can't wait to leave," the donor said.
Another Clinton-leaning person who was in the room said after the meeting wrapped up that there is still "a lot of anger" toward Obama among the New York senator's wealthiest fans.
"It was pretty bad," the source said. He said donors were joking that the scene was like "an Irish wake" and that you "could cut the air with a knife" it was so tense in the room.
Settling Scores, Retiring Debts
The former rivals showed solidarity and then Obama showed Clinton the money, pledging to use his fundraisers to help retire some of Clinton's more than $10 million in debts. That vow drew a standing ovation from the crowd.
He and his finance chair gave Clinton's campaign chair, Terry McAuliffe, personal checks.
Of the dollar amounts, McAuliffe said "They maxed out."
The meeting was a step towards reconciliation, but the wrangling over just how much Obama will help Clinton with her debt is not over. And Bill Clinton's quiet shadow looms. The former president has yet to say one word of praise for the man who beat his wife.
Many Clinton donors are anxious to hear more about Clinton's future role in Obama's campaign, at the Democratic convention in August and whether her delegates will be allowed any kind of symbolic vote on the convention floor.
Asked Thursday night if there would be a roll call vote at the convention in Denver, Clinton and Obama exchanged glances, with Clinton smiling, and said that was still being negotiated.
ABC News' Jennifer Duck contributed to this report.
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