If you read the magazines pertaining to pro audio (such as EQ or Recording or Mix), you know that a recent trend in audio has been to create microphones, often with professional quality, with built-in preamps and analog-to-digital converters and USB output cables. Such microphones enable one to record digital audio directly to one's computer without having to go through the computer's built-in (and sometimes inferior) sound board, and without having to invest in a bulky digital audio interface.
Examples of such USB microphones include the Blue Snowball, the Blue Snowflake, the Samson C01U, the Audio Technica AT2020 USB, the stereo Alesis AM3 and so forth.
Such microphones are usually very simple to use, but what they offer in terms of simplicity, they lack in terms of flexibility. The selection of available microphones is fairly limited. An additional drawback is that such microphones only feature USB output cables, so they can't be plugged into standard mixing boards, PA systems, self-contained DAWs (Digital Audio Workstations), handheld digital field recorders (such as the excellent and affordable Zoom H4n, which has dual XLR mic inputs with phantom power for condenser microphones), a limited number of instrument amplifiers which have XLR mic inputs, and other devices which require traditional analog audio inputs.
The next step up is to buy a separate in-line adapter which enables one to plug a standard microphone into a computer directly by means of the USB port. Such a unit is more flexible, because it would enable one to use offbeat microphones such as boundary microphones (such as the Audio Technica U841A, which would be a good choice for recording numerous people seated around a conference table), shotgun mics (such as the Audio Technica AT4073a, which would be great for recording unamplified speakers from a distance), gooseneck microphones, hanging microphones, headset microphones, instrument microphones and more. Also, such adapters ought to enable one to input guitar, bass, keyboards, etc. by means of "direct boxes".
Up until recently, the best adapter of this type was the Centrance MicPort Pro. (The AxePort Pro is a similar Centrance product for guitarists and bass players.) It's still an excellent product, as far as I can tell, although I haven't personally used one.
Now Shure (one of the most widely used and respected microphones in the world) has introduced a very similar product (to be available this spring)known as the X2u XLR-to-USB Microphone Adapter.
I know of a couple of other inline XLR-to-USB adapters (the Blue Icycle and the MXL MicMate Pro). They don't seem to be quite as full-featured, but at least the new MicMate Pro improves on the original MicMate by offering a headphone jack with its own volume control. There's also a line level version of the MicMate.
Another option: Alesis makes the MicLink for dynamic microphones and the GuitarLink for instruments. The company also offers the LineLink, which is basically similar to the GuitarLink except that it's equipped with dual 1/4" plugs, not just a single 1/4" plug.
There's also a Griffin USB Microphone Adapter, but it's for low-end mics with 1/8" output cables, which is fine for some purposes but not really suitable for professional condenser mics or for most professional dynamic mics.
For people wishing to connect multiple microphones, there are numerous solutions (which I won't cover here for now), if one is less interested in portability than in versatility. But the aforementioned microphones and mic adapters would enable one to easily record pro audio directly to notebook and laptop computers without the need to carry much additional gear. That's especially useful if one's primary need is for recording voice (e.g., blogs) or for making simple music recordings which don't require the simultaneous use and control of numerous microphones.