IPS
IPS (in-plane switching) was developed by Hitachi in 1996 to improve on the poor viewing angles and color reproduction of TN panels. Most also support true 8-bit color. These improvements came at a loss of response time, which was initially on the order of 50ms. IPS panels were also extremely expensive.
IPS has since been superseded by S-IPS (Super-IPS, Hitachi in 1998), which has all the benefits of IPS technology with the addition of improved pixel refresh timing. Though color reproduction approaches that of CRTs, the contrast ratio remains relatively weak. S-IPS technology is widely used in panel sizes of 20" and above. LG and Philips remain one of the main manufacturers of S-IPS based panels.
AS-IPS Advanced Super IPS, also developed by Hitachi in 2002, improves substantially on the contrast ratio of traditional S-IPS panels to the point where they are second only to some S-PVAs. AS-IPS is also a term used for NEC displays (e.g., NEC LCD20WGX2) based on S-IPS technology, in this case, developed by LG.Philips.
A-TW-IPS Advanced True White IPS, developed by LG.Philips LCD for NEC, is a custom S-IPS panel with a TW (True White) color filter to make white look more natural and to increase color gamut. This is used in professional/photography LCDs.
H-IPS Released sometime late 2006, was the H-IPS panel which is an evolution of the IPS panel which improves upon its predecessor, the S-IPS panel. The H-IPS panel can be seen in the NEC LCD2690WUXi, Mitsubishi RDT261W 26″ LCD, Planar PX2611W[2] and Apple's newest Aluminum 24" iMac.
So to sum up, the pros/cons of the H-IPS over the S-IPS:
Pros:
Much less backlight bleed.
No purple hue visible at an angle
Backlight bleed improves looking at an angle
Less noise or glitter seen on the panel surface (smoother surface)
Cons:
Still some backlight bleed in areas that are green.
Viewing angles may have sacrificed in order to improve pros.