Audioengine 2 (A2)

Fig.5 Audioengine2, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the nearfield responses of the port (red) and woofer (blue) plotted below 700 and 300Hz, respectively, and the complex sum of the nearfield responses plotted below 300Hz (black).

Fig.6 Audioengine2, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

These loudspeakers are very cute, but have well balanced response and relatively deep bass extension considering its driver unit size. But be careful that such bass extension is due to strong electronic amplification (see below).

Fig.2 Audioengine2, built-in amplifier frequency response at 1V into 8 ohms, measured at right-channel speaker output jacks (2dB/vertical div.)

Source: http://www.stereophile.com/content/audioengine-2-powered-loudspeaker-measurements

Creative GigaWorks T20

If one is looking for very budget-wise (<$100) but do not want to lose acoustic quality too much, Creative GigaWorks T20 is something he/she must consider. Their vertically-angled design is also highly useful when they are placed on the desk without any external stands.

Source: http://www.ixbt.com/multimedia/creative-gigaworks-t20.shtml

Mackie HR824

Pretty low distortion in bass is impressive. Directivity pattern is also excellent. Very linear free field response  on 50-20000Hz range. Without any doubt, these loudspeakers are very credible equipment not only for studio monitoring but also for serious music listening.

Source: http://www.gearslutz.com/board/so-much-gear-so-little-time/514514-berhinger-truth-b3030a-monitors-2.html

Edifier R1900 Tiii (1900T3)

Semi-anechoic response

Horizontal directivity

Who can blame these loudspeakers considering its amazing price? :)
But be careful that the frequency chart is 1/3 octave smoothed, which I think resolution was seriously damaged. The critical bandwidth of human ear is known to be 1/6 octave these days.

Source: http://en.goldenears.net/index.php?mid=GR_Speakers&document_srl=8756

Genelec 6010B

On-axis and off-axes free-field responses

Flat on-axis response but there seem several (small though) dips. Directivity pattern does not look great for the price range.

It seems that these loudspeakers will perform much better if used with table stands.

Source: http://www.genelec.com/documents/opmans/Genelec_6010B_op.man.pdf

Berhinger Truth B2031A

A bit high distortion at low-bass. But fairly flat response and semi-controlled directivity pattern seem really great for the price range. I guess that's why this monitors are loved as budget-wise mixing monitors.

Source: http://www.gearslutz.com/board/so-much-gear-so-little-time/514514-berhinger-truth-b3030a-monitors-2.html

HiVi(Swan) D1080-iv

Free-field Response

Acoustic Contribution

Horizontal Directivity (0, 10, 20, 30 degree deviations from on-axis)

Vertical Directivity (0, 5, 10, 15 degree deviations from on-axis)

Very flat on-axis response for the price bracket, but directivity patterns are not very controlled thus the sweet spot might be pretty challenged.

Source: http://info.av.hc360.com/2011/11/251504393909.shtml