Yo Fox! The 3.5mm input on either Tascam is designed for a self-powered stereo mic. Most of the really cheap ones, such as:
http://www.8thstreet.com/product.asp?ProductCode=24889&Category=Microphones
probably aren't any better than the mics built into the Tascam units, but they can help to decrease handling noise, as it won't pick up when you are pushing buttons. There are more expensive units of this type that will produce better sound, such as:
http://www.8thstreet.com/product.asp?ProductCode=60280&Category=Microphones
For a good compromise, I've had very good luck with this- I think it's discontinued, but a lot of places still have them, and you can find them on ebay for about $150:
http://www.fullcompass.com/product/301458.html?utm_source=Yahoo&utm_medium=ssp&utm_campaign=trld
That's one of the main reasons I like
Zoom H4n, not just because it can record 4 tracks, but because it has XLR inputs, and can provide phantom power. You can plug whatever mics you want into it. The older
Zoom H4 can do most of the same stuff, but it is a fragile and not particularly reliable unit. H4n was designed to correct pretty much all of the flaws of H4. I did a lot of research, and I think the H4n is the best machine out there without spending a ton of money. So far, it has performed flawlessly in the field. My only warning is to keep it packed with fresh dessiicant, as in humid environments, condensation can form on the diaphragms of the onboard mics. This can happen to any mic, but the small diaphragms of electret stereo mics like that don't take much condensation to mess them up. You can dry them out, but that won't help you if you are trying to record something *right now*.
I characteristically use the Zoom with its own mics for off-the-cuff spontaneous sort of work, or a pair of AKG C2000B's whem I'm trying to do a critical recording. I have better mics available (Neumann KM184's), but I'm not about to use them in a field environment- I'm afraid I work for a living.
I would say, if you are committed to either of the Tascam units, try recording with their own mics before you spend money on external mics which may not be any better. Better yet, just consider
Zoom H4n, which gives you onboard mics, and the option to plug in whatever mics you want. Look for ebay deals on new units that come with all the accessories. I paid $329 for mine, and it came with the plastic case (pretty cheap but compact), the remote control (good for reducing handling noise when using the onboard mics). the handle/mic mount (again, reduces handling noise, and allows the unit to be mounted to a standard mic clip), wind screen (standard accessory-often necessary outdoors) and a 16mb SD card. It comes with a 1gb card, which is fairly useless, but will support up to 32mb cards, which is more than I am ever likely to need in a single session. Thats something like 11 hours of stereo recording at 24bit/96kHz. It downloads its WAV. files to the laptop for backup quickly, and with no problem.
The only downside I've found is that if you are recording in 4 track, you can only use 16bits/44.1 kHz, and most of its FX, with the exception of the limiter and rudimentary compression, can only be used in 4 track mode. But mostly I only use it for field stereo recording, where I don't need a lot of FX, amp modeling, etc. The Zoom also has a 3.5mm stereo jack for external stereo mics such as the ones above, but that does disable the onboard mics. The XLR inputs are also combo jacks, and can be configured to accept a line level signal from an external preamp, or as an instrument input for guitar/bass. or a transducer equipped instrument of any kind.
The H4n also functions as a USB powered audio interface, and comes with the Cubase software. For many beginners, I believe it is a far more versatile and effective unit than a basic USB interface.
Best of luck-Richie