In general, recorders have become far cheaper and most have become better as time has passed and advances in technology were made. In the early days of wildlife sound recording, heroic individuals hauled equipment weighing nearly half a ton on carts to record the sounds of nature - nowadays you can record at a quality matching the best with a recorder held in the palm of your hand.
At the time of writing (2016) the best choices when buying new are found in digital solid state recorders, mostly using SD cards or CF cards. Tape (analogue and digital) and minidisc are obsolete - you can make good recordings with such equipment but you wouldn't start there now. Recorders are made along a wide price spectrum ranging from basic stereo handheld recorders with builtin mics all the way to multitrack recorders with professional P48 balanced inputs. You can make good recordings with the basic models as long as the mic inputs are low noise enough, what you get with more money is greater ease of use, greater flexibility in the range of inputs and mics you can run without ancilliary interfacing boxes, more rugged construction and durability.
The original edition of this guide referred to HiMD recorders. which were a good choice for a modest cost of £150 to £250. at the time (2006), but the market has definitely settled on the SD and CF card recorders since then. At the time of writing (2016) you have a wide choice of solid state recorders.
Everybody initially wants to use their smartphone, but smartphones are jack of all trades and master of none. Assuming that your smartphone does have an external headphone/mic jack, the microphone input is usually only monaural, and the inputs are designed for speech levels from a human at about 10cm away rather than a bird 20m distant, so weak signals and low noise are not a priority. You can get dedicated outboard gizmos to attach to your phone that work around these problems, in which case you are using your smartphone as an extremely power-hungry user interface and storage card.
Solid state recorders are attractive for their compactness and lack of mechanical noise. There is a bewildering array of solid state recorders on the market, and only some are suitable for wildlife sound recording. The next page describes the essential features you will be looking for.
A good start is a handheld recorder with builtin mics. The Olympus LS-10, Zoom H2 are examples of these, but there are many more. Handling noise is a big issue with handheld recorders, though you can eliminate it by putting them on a tripod or using external microphones. You'll always suffer from button clicks when adjusting record level or starting and stopping the recording if using these with the internal mics, but these can be trimmed out on editing.
If you know you will be wanting to use professional P48 powered microphones then you will be looking beyond the entry level handheld recorders to products aimed at the professional market. These will be bigger but will feature balanced phantom-powered microphone inputs, and low noise mic preamplifers to match good microphones
With all modern recorders, but particularly with those where the recording facility is not the primary function of the recorder, you should bear in mind that the low sound levels in wildlife sound recording are a minority interest. Commercial pressures often drive the quality of the microphone stages down to levels that are not satisfactory for wildlife sound recording.
Specifications can be misleading - for instance the signal to noise ratio is usually specified with the microphone input driven at maximum signal level, so the noise is at its smallest compared to the signal. The problem with that is you need to be recording a rock band, not a robin, to achieve these levels in practice!
You can use older alternatives if you have them already - some cassette recorders can be used successfully, and DAT recorders in good working order will give you good results. Open reel was a stalwart of wildlife sound recording for a long time, though you will find the equipment quite large and a lot heavier than a solid state recorder!
Any recorder you get must have the option of manual recording level setting, and some kind of display of recorded level. It must also have a microphone input. It needs to be designed for music recording, rather than speech recording. You should confirm that the device is capable of recording in at least CD format  before considering it. If you see the format described as ADPCM you are dealing something pitched as a voice recorder. It is preferable if your recorder gives you the option of recording uncompressed, and this is mandatory if your aim is to do scientific research into vocalisations using the recordings. It is not absolutely required if you are trying to match what you hear with recordings or recording for the aesthetic qualities. The original Minidisc format, although compressed is well worth considering at an entry level, and the recorders can be had cheaply on the secondhand market. Let us next take a look at the essential features of a recorder suitable for the wildlife sound recordist.
Essential recorder features