There definitely were. It is the topic that dominates English political discussion from around May of 1649 up til Cromwell finally quashes it in 1657.
Charles I is beheaded in January 1649, around the same time that Thomas Fairfax, Lord General of the New Model Army, is getting out of politics and returning to private life (the two are related.) At this point it is clear to everyone that Oliver Cromwell is the true ruler of England because he rules the army, which had previously overthrown Parliament in a coup in order to bring about the king's execution. Pride purges the Long Parliament, more or less the same MPs from the start of the war, and what he leaves behind is derided as the Rump Parliament.
Different factions have widely varying views about what should happen next. There are firm republicans, "commonwealth men," like John Bradshaw (who was the judge at Charles' trial), or John Milton (Milton changes his mind a lot to better suck up to the powerful, but in 1650-53 he's a republican,) and most anyone associated with Fifth Monarchism. It's important to note though that these people largely agree that Oliver Cromwell is the person most capable of establishing their Protestant republic. They support him. After all, the world is full of dangers (Scots, Presbyterians, Irish, Papists, Charles II etc.) and the only way England can establish a republic that will be a beacon of "liberty" through the Protestant world is by securing the power of the state against its enemies. There's no reason a Commonwealth can't have a protective first citizen, at least for a while, until it's safe to call a new parliament. Julius Caesar could have been a great man, had he returned liberty to the senate, and that's what republicans hope to encourage Cromwell to do.
Milton in particular supports Cromwell because Cromwell is for liberty of conscience. Cromwell famously said that he "would rather Mohamedanism be permitted amongst us, then that one of Christ's children be persecuted." Milton fears that Presbyterians will establish a state church and disallow liberty of conscience, Cromwellian government is his shield against that threat. In the true fashion of an early modern scholar he writes Cromwell a celebratory poem brimming with advice.
Cromwell, our chief of men, who through a cloud,
Not of war only, but detractions rude
Guided by faith and matchless fortitude
To peace and truth thy glorious way hast ploughed,
And on the neck of crowned fortune proud,
Hast reared God's trophies and his work pursued,
While Darwen stream with blood of Scots imbrued
And Dunbar field resounds thy praises loud
And Worcestor's laureate wreath; yet much remains
To conquer still; peace hath her victories
No less renowned than war, new foes arise
Threatening to bind our souls with secular chains:
Help us to save free conscience from the paw
Of hireling wolves whose gospel is their maw
The tricky thing for these republican Cromwellians is that his rule doesn't have an expiration date and it's not clear how it can be ended. In 1653 there is an attempt to replace the Rump with a new, hopefully more legitimate Parliament, but this doesn't work because even though Cromwell gets to handpick the MPs there are different factions among them and they don't agree about anything.
Cromwell forcibly dissolves Barebone's Parliament, calling the MPs "whoremasters" among many other things, and is once again simply a military dictator.
From the perspective of many people Cromwell's government is more abitrary than Charles I's ever was. If a major grievance had been Charles' refusal to call parliaments, how now does England exist under a government that does not think parliaments are legal? Offering Cromwell the monarchy quickly becomes a way to get him under the constraint of some kind of law. England's traditional laws recognize a king, and the boundaries of a king's powers. As it stands Cromwell has been free to make up his own rules as he goes along, making him King would put him within familiar framework.
When Cromwell institutes the military government of the Major Generals these people offer the Humble Petition and Advice, suggesting Cromwell be made hereditary Lord Protector (he wouldn't hear of "king") in exchange for agreeing to call regular parliaments, reduce the army, and reduce the unpopular high taxation that pays that army.
Cromwell refuses. Why is a very debated question and I've written enough already that I doubt I'd do it justice. He accepts a modification of the advice securing succession for his son Richard, but not any of the constraints on his power. This certainly contributes to the lack of support for Richard in 1660. Had Cromwell settled the country in a more permanent way, had he negotiated a fixed system of government, the Restoration would have been at least much more difficult.
As for sources, the poem I transcribed from Blair Worden's book which I fortunately had near to hand. I'd recommend it highly. For general sources on 17th c. England I put together a brief reading list on another response