I'm getting ready to buy night sights for my Glock 20.  I'm looking at either the Meprolight($65) or the Trijicon($90).  Any preferences?

I got the Trijicon's on my Bushmaster and I love em' they are really bright in pitch black darkness, the darker it is the brighter they are (mine are green but i think you can get different color's like a green one in the front and 2 different color's in the back or vise a versa to get a better alingment at night or something I guess, in the daylight they look white it's like an alignment thing. I'm not sure about the other brand you mention.

I use Trijicon on my Glock and AR, and am happy with them. However, there is not a nickle's worth of difference in Trijicon and Meprolite sights. The Trijicons are a little smaller (the dot that is). Either way you go, I think you will like 'em !  

Yeah my wife has a Kahr P9 with Trijicon sights, and I've got a SigPro with their version of night sights on it.  The only difference I can see in those two, is that the Trijicon has a larger front sight dot than the two rear dots.  I find this is helpful in aiming.

I have Trijicon's on my Glock 23 that I bought a few years ago.  Went with the Trijicon because (at that time) the tritium was outlined in a white ring which aids day time shooting.  

This was pretty much the only difference though.

I just bought two sets of IMX sights from Lone Wolf Dist. they have bar dot configurations, and reasonably priced around 65$. They are very bright and have 10 yr. warranty.

I have both Meprolights and Trijicons on my Glocks and I'll have to agree with LAcop on this...there's hardly a nickle's worth of difference between the two.  The Trijicons have slightly smaller dots, but both brands have white outlines for daytime use.  Conversely, because the Mepros have a larger dot, I find the sight picture easier to acquire in the dark because they stand out better.  Over all, equally effective in my opinion.  You can't go wrong with either.

One more thing, if you're buying night sights separately, make sure you get the ones designed for the G20/21.  They are different sized than the 9mm/.40 ones.

Consider the Ashley Express sights. I got the standard size dot with night sight inserts (front only) after looking at all the others mentioned here.

They're fast and a little less precise for longer ranges (25+ yards) and bullseye. That's why they make great carry sights.