Erika Smith. I actually have used this pseudonym when checking into a motel anonymously. It’s kind of generic but unusual enough to be plausible.
Chao Wong
My doctor’s office building used to require people to sign in and out if you arrived after 5pm. I changed based on the day - sometimes I was E. Dickinson, sometimes B. Ross, sometimes D. Prince, sometimes I. Rasputina, sometimes N. Tendo.
It amused me.
Vice-Chancellor Ozone.
Washington Irving. Or Irving Washington.
Probably something like John Smith. Or maybe just “James [mylastname]”, since there are a lot of those around here, and my middle name is James.
Now that I’ve finally found a good anagram of my name, I’d use that.
No, I’m not going to tell you what it is.
Never thought much about it, but when I wanted to lie for whatever reason I’ve used Maria as my first name; Marie is my middle, sooo…close enough.
But now I am surrounded by so many Marias that most of them go by their middle name, so I’m no longer sure I’d answer to it.
Will have to come up with something interesting! Knowing me, I’d use my common game name, Taolynn Mist. Sure, it sounds made up…and it is! Maybe I should start using it lots just for giggles, and see if anyone ever thinks it’s cool enough to actually name their kid that.
ETA: looking at some of the other answers, I now want to use a Bond girl name; if it gets any eyebrows, just say your dad was inspired. 
Phil McCracken
I have a simple pseudonym that’s easy for me to remember. See, my father had his heart set on naming a daughter “Sarah” but that’s not what I ended up with. My father-in-law’s parents got divorced after about 10 years of marriage, and after his mother re-married, his stepfather legally adopted him. So I just use what my last name is “supposed” to be … King. Sarah King is a perfectly innocuous, normal sounding name that no one would suspect to be false.
Last half of my mother’s middle name, her maiden name.
The name that everyone knows me by is actually my middle name; it is also a not-unusual last name. So when I was a radio DJ in college I dropped my unusual, longish last name and just used First-Middle instead.
For example if my name was Joseph Bradley Worzceski, my friends called me “Brad” but I used the radio name “Joe Bradley.”
Hal Briston.
I’ve used it for things along the lines of checking into a hotel anonymously before…
Eric Thomas (think about it)
Harry Palmer, pseudonym of the protagonist in the Len Deighton spy novels.
“Art” is the name I give at restaurants when I have to wait for seating. It’s an old nickname of mine and it comes in handy because my both my given and family names are common.
I’ve never had the urge to check into a hotel using a false name. I guess my life is dull.
I’ve used my name here IRL many times. It never gets any comments.
This is my third name on the SDMB, my first was my real-life first name.
Years ago there was some sitcom that I only saw one episode of, but it’s always stuck in my mind that the wife was telling the husband that she had a standard pseudonym (“Barbara Bishop”) and was surprised that he didn’t have one himself.
I don’t have a standard pseudonym, but once or twice I’ve identified myself as “Patty” when some weirdo on the bus wanted to know my name and it seemed easier/safer not to simply refuse. There’s no real reason for that particular name, it just popped into my head. I think it’s a good fake name though, because it’s ordinary enough not to seem suspicious.
*El *Gatopescado