I have a Gen4 G26. (Subcompact, new rough texture frame, backstrap addon options.) It's my every day, concealed carry gun; I haven't owned many other guns but I've held and shot a lot of other guns. J-frame revolvers, 380 pocket guns, commander sized 1911's, and although I liked them all I wouldn't trade in my G26 for any of them any day of the week.
There are SO many options for modifications. Most of them are "just for fun" or "would be nice", but IMHO there are two (well, technically three) things that complete the G26 and turn it into the perfect concealed carry gun: the first and most important is a set of magazine base plate replacements from
GAP Enterprises. It's not one of those extensions that makes the gun longer, or adds length to the grip - it just extends outward to give your ring finger something to rest on. Doesn't look like much but it makes drawing from an IWB holster so much easier, and gives a little extra control on followup shots. The second (and third) is an IWB holster and a pocket holster, I very strongly recommend both from
Raven Concealment
As for would-be-nice, a lot of people don't like the idea of replacing the recoil assembly with a Lasermax guide rod, or becoming too reliant on a laser, but I think it's a nice added bonus. I wouldn't say it needs it though - I treat it as a backup sight, rather than a primary. Lastly, they make magazine sleeves that can slide over the full-size high capacity mags that basically turn the gun into a short-barreled version of the full size glocks.
On a side note, I've often wondered if the Glock 26 slide could be milled down for a trench sight. I'd get rid of the iron sights and go trench with it in a heartbeat, but I'm just not sure if there's enough slide there to cut away. Plus the way the barrel shroud fits in, you'd have to mill part of that away as well.