The AT 845 is an excellent stereo mic, can be handheld or camera mounted.
Microphones built onto a camera fall into the "next to useless" category. They are great for soccer events, events where the crowd is the action, and spaces where good audio isn't important. That's all.

If you're serious about the word "good," then I would recommend the little Sony ECM-MS908C, a stereo mic selling for only about $80 on the Internet. It has a miniplug connector, though.

One will never mistake the output for that of a $1,000 microphone, but for my on-the-move recording it works great, since the ambient noise level is usually far above what the mic adds.

Some internal camcorder microphones are, to my ears, surprisingly good (flat, wide, minimal camcorder whine). I suspect the Sony guys have spent a lot of time on this issue in some of their camcorder product lines. One thing I've read is that those camcorders having internal mics that face upwards are far worse than those facing forward.

Keep in mind always, it's a proximity thing. I submit and can easily demonstrate that a $5.00 stick-on computer microphone that is 2 feet from subject is far better than a 300.00 mid-quality mic on a camera will be at 15 feet from subject. Almost none of the on-camera mics have shielded cables running from the mic to the preamp. this is because the mic cable usually run through the handle of the cam, and therefore must be flat. Hard to weave a flat braid.
Mics ON the camera do exactly what they are supposed to do, pick up what's around the camera. Thumbs popping the record button, zoom lens noise, operator breathing, these are all evident on a camcorder mic in most scenarios. If you want to look at much better, but still rarely acceptable by most standards, get a Lightwave mount and an AT 897 or 835ST. These are good mid-level mics, great guns in the sub 1K category. Better still, get an AT 899 or Sony ECM 66 lav mic, very hard to beat.
Mics need to be close to source. Like a hand grenade, a mic does it's best work close to the subject. Proximity. It's a good thing in a mic.
The type of plug has no relationship to the quality of the mic. I've got several Sennheisers that have been modded to output to a 3.5 mm jack, and a couple ECM 55's that have had the same mod.
Audio is deadly critical. So much more so than video. Get it good the first time. Keep the mic off-camera whenever possible. This is one great thing about the 845, it's far 'better' than the typical 'good' on camera mic, but is wonderful when placed close to subject. Mono is the real answer for most situations though...if it's an interview, cap mono, not stereo. Phasing issues go away when you cap mono.

I used the word "good" as a shotgun thing (Not the mic). Spot, I'll check out the microphones you mentioned. I mentioned the XLR plugs because I thought the Mic has to have that too or do they make adapters? Somwhere in the back of my mind I think yes, but I would like info on that too. Two mic's in time since the DVX100a has two XLR jacks if my memory is correct.

The only time you "need" XLR is when you have long cable runs, longer than approx 10 feet. Low impedance connectors and cables are required for any length to prevent noise.
There are many different XLR to 3.5 mm (1/8 mini) connectors, they are cheap. Sometimes you'll need a preamp, depending on the camera's built in pre's. The PD 150 for instance,was very well known for having a noisy pre, but there are companies that mod this cam to have a great pre. The PD 170 doesn't have this issue.
Canon XL1 has a noisy pre, so we use a Beachtek most of the time, the GL2 doesn't suffer this. You can always buy a beachteck or Studio device to convert lo impedance (XLR) to high impedance (mini) at the camera too.

XLR minimizes noise because it is balanced -- 2 signal lines referenced to a 3rd ground. Unbalanced (coax) is a little more likely to pick up noise but should be fine for moderate length runs in typical environments.

You can get adapters to connect xlr to unbalanced. The simplest just connects one of the XLR signals to with ground. It is a direct wiring between the XLR and balanced cable. For best noise performance they make adapters with transformers in them, but you probably won't really need it.

If you can get an XLR mic just stay with XLR for the DVX100. One advantage is that the DVX will feed 48V phantom power for mics that need it.

Audio Technica makes great microphones. (I love the 899 lav.) I use the AT-825 for stereo field recording and the AT-835ST when I need a little more "reach." Both are excellent sounding microphones. The stereo capsules are so well matched that one can "mono" the channels in post and have no phase cancellation issues. The 825 is strictly a L/R stereo mic and the 835ST can be run L/R or you can use an M/S matrix so you can play with the stereo imaging in post. The AT-822 is an unbalanced version of the AT825 and is less expensive. It's simple enough to build an XLR "breakout" cable for the 822 and use it with balanced inputs.

AT-825

AT-835ST

John

Been using AT825's for years myself and they're pretty low noise, clean sounding, and not too expensive. But a lot of folks seem to be going with the slightly more expensive Rode NT4 lately.

Howard

My AT-825 has always been good to me. I've done lots of different
types of recordings and it has always sounded as good or better
than my other equipment.