Yeah, don't become an "L-coholic". A lens doesn't have to be an L to be good. About half my lenses are Ls, the rest aren't. Buy the focal length and features that meet your needs best, who cares if it has a red stripe on it or not.
If you are a wedding photographer or portrait photographer, the 50L or 85L might be just the ticket. If not, a 50/1.4 or 85/1.8 might be a better choice for general purpose shooting.
A lot of folks really like the 100/2.8L macro... But for me the 100/2.8 USM is a better choice. Most of the time for macro I'm using a tripod or monopod anyway, so the IS that the L brings to the table really doesn't do a lot for me. So, rather than spend $400 extra for the 100L, I spent $160 for the tripod mounting ring for the 100/2.8 USM.
Besides, the build of the 100/2.8 USM is identical to that of the 180/3.5L. The 100mm just doesn't need exotic glass (part of how Canon defines an L, req'd for it to get a red stripe). I also like that the 100/2.8 USM shares 58mm filters with several of my other lenses, where the 100L might require me to get some 62mm filters.
Another example, I have a couple Tilt Shift lenses... one is an L the other isn't. Yet they are absolutely identical in build and, if anything, the non-L offers slightly better image quality. Once again it's a situation where the non-L just doesn't need fancy glass to do its job very well, so doesn't meet Canon's criteria and qualify to get a red stripe painted on it.
Some Ls are excellent and unique. With others there are very good and capable alternatives.
I'll likely never own a 24-105L.... a 28-135 costs 1/4 or 1/5 as much and gives nearly identical image quality. It's also close focusing, fast focusing and nearly equal in IS performance. It's just not as well built/sealed. But, hey, they both get "zoom creep" (the 28-135 is probably more prone to it) and for the money, I'll take the 28-135 and be happy.
If you're holding your breath for a 24-70/2.8 with IS.... well, good luck with that. The 24-70/2.8 II was intro'd within the past year. The previous model was intro'd in 2002. So you might expect the next update in approx. 2022... and who knows if Canon will ever add IS to it. There is the new 24-70/4 IS coming soon... which might be a good match with the 6D in particular. Otherwise, there's the Tamron 24-70/2.8 VC. But, frankly, I use a 24-70 and see little need for IS on it. 24-70 is a pretty large and cumbersome "walkaround" lens... I often use the 28-135 instead when I want to travel light. My favorite use for the 24-70 is as a portrait zoom on a crop camera. It's a little short for portraits on a full frame camera.
I love the 135/2L on my full frame camera. I've always enjoyed using that focal length, but for a long time was only using crop sensor cameras. The day I ordered my 5DII, I ordered a 135mm to use with it.... I knew I'd want it and it hasn't disappointed. It'd be nice if Canon would update the 135 with IS (it's considerably more beneficial on a telephoto like this, IMO), and perhaps with a curved blade aperture... but there's really not a whole lot to improve.
Tell us more about your purposes, needs, as well as what other lenses you have and what camera(s) you'll be using them upon, and perhaps we can give you better recommendations... tho they might or might not be Ls.
My "first L" was actually four lenses: 17-35/2.8L, 70-200/2.8L IS, 300/2.8L IS and 500/4L IS. I was switching from another camera system and shooting film at the time (initially with a pair of EOS-3s). I still have three out of those four lenses. I've added a number of other lenses over the years since, as needed... both L and non-L.