úmëa ér uilë - Evil still lives?

Well, Sauron didn't have a lieutenant that served him as he served Morgoth. Arguably there were the Nazgul, but after the One Ring was destroyed, they were gone along with Sauron.

Durin's Bane had been hiding since the end of the first age, nigh 8,000 years, IIRC.
Most of the Balrogs were destroyed in the war of wrath, and are more intent on hiding then ruling Middle Earth. If they had any ambitions like Sauron did, they would have been more present in the second and third ages. As far as I can tell, the Balrogs were used more like Elite troops then battlefield commanders.

[Sharkû]

There is no evidence whatsoever that more Balrogs survived the Fall of Angband. Tolkien states in a letter something to the effect that 'here we find one that one has survivied the Fall and hidden', implying he was the only one to do so. Implied or not, we know of no others.

Personally, I have also argued in the past that there were no more Morgothian dragons after the death of Smaug.
Of course Shelob might still be around...

What we know of the evil in the 4th Age is that it mainly comes from the inside, from Man's dissatisfaction with good, resulting in youths playing orcs, secret cults etc.

[Knight of Gondor]

The appendices of RotK speak of the remaining evil creatures that had to be routed out and killed by King Aragorn and King Eomer. The ruin of Mordor was left alone, lest any of the evil that dwelt there be disturbed, or something like that. That's one of the things that always bothered me a little about Middle-Earth...you never do defeat the evil entirely. Morgoth came back from being chained, then Sauron stayed after Morgoth's exile. Then Sauron was destroyed, but wasn't fully gone. Then he was finally destroyed...well, we don't know much beyond that.

I agree, though, the primary evil after Sauron's fall was in the weakness of Man.

[Kransha]

Well, generally, Melkor/Sauron's evils have been extinguished. Orcs linger in the Misty Mountains, some orcs may remain around Nurn, there are always a few bothersome trolls, Haradrim, Easterling, and Dunlending rogues. Various villains to be dealt with, but no really great evil. Eomer and Elessar rode out in the 4th Age to quell those evils, though many of these exploits are yet undocumented.

Actually, there are two loopholes. Firstly, the forgotten 'Citadel' of Gundabad, the orcish stronghold in the Misty Mountains, which survived the War of the Ring and must be thwarted. Secondly, the slim (very slim) possibility that there are lesser dragons or the 'worms' of the east that are sparsely mentioned. This is, of course, nary more than heresay and conjecture.

For an illustration of possibilities, look to The New Shadow, the barely satiating first chapter of a possible sequel, written by Prof. T. himself. For good reason, JRRT gave up on this, seeing it to be pointless to explore man's weakness, since the Third Age Myth for Britain was already complete. Man's weakness would be nothing but a weak allegory for the Medieval world, not fantasy in any respect and not really Tolkein quality.

In that brief glimpse, we are only introduced to preliminary characters, one being Borleas, son of our RotK friend Bergil (or was it Beregond?). It is unsure whether he was meant to be the protagonist, and the story only falters, despite the usual Tolkein flourish of the writing. It is shown that all evils will arise when man's world succumbs to generic corruption, like the abovementioned cults, etc.

[symestreem]

There will always be evil, because of mannish nature, and dwarvish nature to a lesser extent. Even if all of the bad creatures were hunted out and destroyed, man would still be treacherous.
Why did Gundabad play no part in the War of the Ring? Was its population decimated to that extent by the Battle of the Five Armies?
Kransha, it's probably Bergil's son; Beregond's son would be Bergil's brother.

[Voralphion]

Gundabad was mostly destroyed in the war of dwarves and orcs when they wanted revenge on the orcs for he killing of Thrain by Azog.

It says somewhere that Sauron was the last personified evil in the world, and that any evil after that would be the evil in men.

[Saraphim]

But Morgoth himself the Valar thrust through the Door of Night beyond the walls of the world, into the Timeless Void ; and a gaurd is set forever on those walls, and Earendil keeps watch upon the ramparts of the sky. Yet the lies that Melkor, the mighty and accursed, Morgoth Bauglir, the Power of Terror and of Hate, sowed in the hearts of Elves and Men are a seed that does not die and cannot be destroyed; and ever and anon it sprouts anew, and it will bear dark fuit unto even the latest days.

This is from the end of the Silmarilion.

It means, at least to me, that although Melkor, and later Sauron, was banished from beyond all the circles of the world, what they strove for (the dominion of Hate and Terror over the children of Illuvitar, ect) was, at least in part, successfull.

When has any of us not felt afraid, or hateful? According to Tolkien, the thought that was planted within the first genrations of humanity still holds true today. So, yes, úmëa ér uilë.