24" IPS LED 120hz Monitor

120hz is currently only available in TN panels (with one exception I know of). Usually 120hz monitors offer active 3d, which requires the worst-case response time (including any inverse ghosting) to be under 8.3 ms to avoid having the image intended for one eye show an afterimage to the other eye. The best an IPS panel can do is 11 ms:
http://www.digitalversus.com/lcd-monitor/ghosting-time-...
11 ms ghosting time probably looks okay on a 60hz screen, but would mean significant crosstalk between eyes if you tried to do 120hz active 3d with it. If you just want the 120hz for smoother 2d graphics, that might work, but none of the major manufacturers offer that standard. The only way I've read about to get 120hz IPS is with an overclocked Yamakasi Catleap - look through this thread for instructions on how to get one and how to run it at 120hz:
http://www.overclock.net/t/1225919/yamakasi-catleap-mon...
I don't know how many overclocked models are still available on eBay, and I have a vague memory that some units were only overclockable to 100hz instead of 120. Also note the screen is 2560x1440, so I think you'd need a high-end multi-gpu setup to get high enough framerates at that resolution to benefit from the higher refresh rate.

Thanks for that reply, it has provided some real clarity! Ok well I think I am going to prioritise 120hz over IPS, as I will be primarily using it for gaming.

Not exactly true. "IPS" is a generic term used to represents all the various types of IPS panels. e-IPS panels are the least expensive type of IPS panel can compete against more expensive types of TN panel monitors when it comes to price. H-IPS and S-IPS panels are more expensive and they tend to have a 6ms response time as opposed to 8ms for the typical e-IPS panel. My Planar PX2611w H-IPS panel monitor has a response time of 5ms due to a slightly more aggressive response time compensation setting. Some monitors do not use response time compensation (RTC) at all so they tend to be advertised as having 12ms+ response times; the Apple Cinema Display for example.

"Rated" and actual response times can differ, but to say that the best an IPS panel can do is 11ms is a bit misleading especially since that is for an e-IPS panel with RTC rather than the more expensive H-IPS and S-IPS panels with RTC.

It is true though that there are no 120Hz IPS panels.

I consider the 11 ms less misleading than the manufacturer response times. If you can provide a link to a review of an IPS monitor with ghosting time measured under 11 ms, I'll accept your correction.