What do you feel is actually appropriate? I don't want to appear as a stiff who won't fit in with the culture.
If you're totally starved for ideas, for guys, khaki pants and a solid shirt, both ironed. I'm even less qualified for giving sartorial advice to ladies than I am to men, so I'll defer to someone else on that.
n.b. I fairly often do meetings with startup folks, including potential clients, in either that or my usual jeans + T-shirt with a track jacket on top uniform, and can't remember feeling conspicuously underdressed recently. (Edited to add: Ahh, forgot a conspicuous exception that proves the rule, but I can't disclose it without violating an NDA. Suffice it to say that if the industry a startup is in would make a blind ferret say "Dude, you should dress up for that" then you should probably dress up for that. Still got the engagement but went shopping before I started showing up on site.)
IMO, a suit and tie, especially for a junior developer type position is probably wrong UNLESS you are the sort of person that is 100% comfortable and natural in a suit, and even then I'd skip the tie.
My goal would be to dress 1 step above the people you are interviewing with. Enough that you clothes help convey a sense of elevated status, but not so much they look at you and go "I don't want to work with some guy that wears a tuxedo to work".
Based on my non-scientific observations over the years, the ideal outfit would be pressed khakis, ironed polo or button-down shirt, sport-coat. If the environment is one where the people dress a little nicer, then you fit in well and the jacket probably sets you apart. If it's uber-casual you can leave the jacket someplace and then you'll be dressed nicely, but still a touch above most of the people you're interviewing with.
FWIW, I can't remember the last time I've work a suit to an interview in probably 15+ years, the last 10+ of that I've been working higher-level management type jobs, many times in sales-ish roles/departments.
Also, respect to your parents, but their conventional wisdom is probably massively out of date with current job trends/cultures, especially as it relates to developer positions.
a suit doesn't necessarily = well-dressed
no suit doesn't necessarily = not well-dressed
But, I do agree with the poster below: If a company balks because you overdressed for your interview it's their problem, not yours.
However if in future I am ever struggling to find a job then I will likely have to relent on this rule.
It really depends on the company, though. If while talking with the company before the interview they came off as lax on their dress code, I wouldn't bother wearing anything fancy. I guess it's about judging the appropriateness for the given situation.
In the end, I'd prefer to wear whatever I'm most comfortable in so I can be myself and show them exactly who I am, as opposed to carbon copy office bitch in a suit.
Unfortunately, my present employer requires I wear a collared shirt and dress shoes, which I hate. I am much more productive when I can wear whatever I want. It shows, too. Especially when I'm forced to come in on a Saturday but can wear whatever I want; I get so much more done.
I do not think that just by wearing a suit, you would give that impression. everyone understands that interviews are always a little more formal than the actual job. Even if the startup company where you will interview has dress code which includes shorts or jeans, I suggest you go in a simple business suit. The worst that could happen ? The interviewers will tell you that they are not that formal but thats ok. If you go without a suit, it may not hurt your chances either especially at a startup but why take a chance. My suggestion: go with a business suit. You have nothing to lose with that.