[kwis]

If you're on FreeBSD you can use dummynet to simulate packet delay and loss.

It's quite handy. My partner has slow, unreliable, high-latency Internet in his house and there are an entire class of performance problems that are extremely obvious when I work from his place that are barely measurable when I work from a 100mb line that's only a few milliseconds away from a major datacenter.

[rimantas]

And if you are on OS X (and have Xcode installed), look into Developer->Applications->Utilities->Network Link Conditioner.

[infinite_snoop]

If you are in the UK you can simply choose Virgin as your broadband provider to achieve the same effect.

[Will_Price]

Or talktalk, I don't even get cable out here in the country...

[robin_reala]

Or if you’re on any OS with Java installed, try Sloppy: http://www.dallaway.com/sloppy/

[rvavruch]

I second Sloppy. I've found it very useful for debugging Flash errors that only happen occasionally. By slowing the loading sometimes them become reproducible. It's also useful to see how a webpage loads on a slow connection - for example: is your copy legible before your background image has loaded?

[yardie]

Thanks! I didn't even realize that was there.