Kestrel gave you a solid start. Different kinds of villains will work best for different purposes. You wouldn't make the big bad evil guy end boss the same kind of villain as a side guy who might be the primary antagonist for the very first story arc.
Aside from that, a lot depends on what kind of world you're making a villain for, with particular emphasis on the kind of morality the world and story aim to present. If you're rolling with a straight up black and white morality then you'd be best served with a villain that's pure evil. If you're going for a full spectrum of morality rather than black and white, then you can get into more ambiguously evil bad guys. Going for full on shades of grey morality means you'll probably want a sympathetic and/or easy to relate to villain, the kind of guys you might actually root for or not see as a bad guy if they didn't happen to be on the side opposing the protagonist. Lord of the Rings has good examples of all of these kinds of villains: Sauron is basically the Satan analog of Middle Earth, pure evil without a doubt; Saruman is sort of ambiguously evil because while he does horrible things he's doing it for a good cause (destroying Sauron), started off with a "the ends justify the means" kind of mindset and then got further corrupted; Gollum is kind of pitiful, a once normal guy who was twisted and corrupted by an evil artifact that he was no match for, so it's easy to sympathize with him and when he's helping Frodo you can really see him as one of the good guys for a while.
Another major component is motivation. You say you make villains who desire power. Okay, why do they want power? Desiring power for the sake of power is pretty much a cliche at this point. Most people who lust after power have an actual goal in mind, something that they need power to achieve. Does the villain want to rule the world? Do they want to destroy it, and if so what is their actual reason for wanting to destroy the world? Does he want to live in luxury? Is he a sadistic bastard who just wants to see people suffer? Does the villain have a goal in mind that is actually a good thing, but he uses evil means to work toward it? Does the villain perhaps have a loved one who is deathly ill and they're trying to get power to achieve the means of healing that person? Having some kind of motivation other than "IT'S CUZ I'M EVIL!!!" and "I JUST WANT POWER!!!" is a great way to make villains not lame.
And then there's the personality. Villains don't have to be pure evil, or scumbags, or assholes, or whatever. The only time your villain should have no redeeming qualities is when it's a straight up black and white morality world and plot. If your world has shades of grey in it, then your villains should too. Take a look at real people who are considered horrible villains for a great example: Adolf Hitler was very polite and charming in social situations and he loved dogs. Just because people do bad things or have bad intentions doesn't mean the entirety of their personality should be evil (unless it's black and white morality, because duh). One dimensional characters are boring, so don't make your villains one dimensional.