Quick – you’ve got a music file that someone (a collaborator, a client, a friend) needs to hear. How do you send it to them?

It seems countless Web entrepreneurs have new ways for sharing media – there are online Flash-based music editing applications, social networks, elaborate MySpace and Facebook killers. We’ve been impressed with some, like the rich player and commenting and fans on Soundcloud or the ability to create artist/band pages that really work on Bandcamp. (The latter, I do really want to spend more time with.)

But sometimes, these services are overkill. This week, I had to get some revised sound scores to a choreographer so he could have them in a rehearsal. I didn’t want to share them with my network of friends or let people remix them in Flash – I just needed to get them to him in the easiest way possible.

That’s where drop.io is just absolutely gorgeous and lovable. Using something else? This is probably better.

1. There’s not even a login. Click a button, upload a file, done. You can add your email address and password if you need to be updated, but even that isn’t necessary.
2. You get an instant short URL – either automatically generated or customizable.
3. Drop any media you want – images, music, etc.
4. You get instant in-browser playing / viewing, and embeddable links and downloads.
5. Control: non-public if you like, expire whenever you want, let others add files.
6. It’s free for basic usage, and the free account isn’t crippled. You get 100MB of space per drop. Need more than that, and you can upgrade, but I think a lot of folks will be pleased with the free plan. Fortunately, the premium plan is powerful enough (branding, bigger drops) that premium users may be able to subsidize the occasional, casual user.
7. Integration: Firefox add-in, Twitter, etc.

In other words, this kicks YouSendIt’s sorry, badly-designed, clunky and non-functional a**.

playlist.io, announced this week, allows easy, playable playlists, so ideal if you have a set of tracks – all with the same features of drop.io

It’s probably not how you want to share video or whole projects. But for a quick audio bounce of your current track, photos of the venue you’ll be gigging at, and the like, it’s about perfect. There’s a place for more complex tools that allow you to collaborate on, say, custom designs for music software or hardware or elaborate session sets. But that makes it even nicer to have a quick tool that solves a simple problem.

And speaking of “tools that get things done up against tight deadlines,” drop.io has added a whole new dimension:

Real-time functionality

The folks at drop.io (who work just over the river from me in DUMBO Brooklyn, that “other” Silicon Alley) have been hard at work on new real-time functionality.

What this means is, you can instantly add media, notes, and chat message, even via a mobile device, and everything is there instantly. So, someone calls on the phone and wants a file. It’s up there instantly, and you can even comment on it, make changes, and get it done.

Speaking as someone who is constantly missing deadlines, um, I mean regularly procrastinating things until the last minute, uh, erm …. uh, always overbooked and dealing with crises … uh, I mean, “moving at the speed of innovation,” this sounds like a lifesaver / problem solver.

There’s no question this is of use to music pros and the ilk. I know the people doing music and sound design for South Park have regularly emailed MP3 files in order to get them on the air on Comedy Central the same day. We’re a “just-in-time” — or, perhaps, “barely on time” crowd, the digital creatives.

I’ll be really curious to hear how you use this, and what other tools are out there you like. And because drop.io is a relatively simple tool, I’m equally interested to see what might be possible with their open API. Let us know what you think.

Updated: Via comments, Kyran notes that Dropbox is also a really strong option. What I like about Dropbox: desktop clients, sync capabilities, easy sharing of whole folders, revisions, and most of the chat features. What I like about Drop.io: stupidly-simple quick file uploading one file + url. Drop.io is to me sort of Twitter-style file uploading. Dropbox is also a really terrific solution. I could actually see using a little of both, which is why lightweight solutions are nice.