In your price range, XLR inputs just aren't going to happen. Do you already have XLR microphone equipment to use? If so, consider an XLR adaptor like the Beachtek DXA-2T. I've had a lot of luck using it for camcorder, HDSLR and my Zoom audio recorder.

In this price range you are looking at basic models with small sensors, so don't expect shallow depths of field shots or great low light performance.

The Canon Vixia cameras are a solid option, with the HF500 being a steal of a deal right now ($200 on sale.) But Sony, JVC and Panasonic also offer cameras in your price range that will do the trick.

Look at the widest viewing angle when zoomed out, whether is shoots 1080 at 60P, and make sure it has the inputs and outputs you are looking for. At this price, you won't likely get a viewfinder, just the fold out screen. All will have digital menus on your touch screen and few external buttons.

This is going to sound a little crazy, but you will be surprised how well it works for online video. Use your iPhone. You can get good external mics designed for them, and if you flip them sideways, iPhones really take surprisingly good video.

Here's the trick: Look at some of the videos on this site about how to shoot and edit video. Only one-third of your video quality depends on the gear you use. Two-thirds depends on how you shoot and edit it.

You wont get on-camera XLR at that price, but you could use adapters. For $275, the 

Canon 8GB VIXIA HF R50 Full HD Camcorder has a mic input. I reccomend upgrading to the Sony a58. It goes for $399 with a lens. This is really more of a DSLR/Mirrorless (an SLT, actually), but if you're willing to accept the DSLR form factor, you will get so much more

Finally, if you are okay with an action camera, the Drift HD Ghost has a mic input, and is waterproof, shockproof, and everything-else-proof. It's around $220

If you don't need HD, then there are lots of absolutely brilliant real professional cameras on ebay – for 300-500 that have lenses on them that cost over 6 grand when new, let alone the camera – Sony DSRs in the 300 and 500 series for silly money. They're simply excellent cameras and despite being SD, look knockout on youtube. You can get some super bargains – all have a full pro spec and plenty of people are still using them for TV stuff.

Dude get a Canon HD VIXIA HG20 if you want a camera with perfect HD video of your youtube vids. This baby can make any of your video's without a hassal, and i should know since I have. Its got 60 GB inside the hard drive, got a plug for headphones and a microphone, plus its pretty medium sized camera with a 12x optical zoom. In short great camera to get for youtube video's its easy to use. But since it works for me it may not for you so look at the reviews on amazon: http://www.amazon.com/Canon-VIXIA-AVCHD-Camcorder-Optical/product-reviews/B001DTTCQA/ref=cm_cr_dp_qt_hist_three?ie=UTF8&filterBy=addThreeStar&showViewpoints=0

Oh by the way its expensive if new so buy it used.

Costs $255.30