I've had and used the Rift plugin (LINK) from Michael Delaney, and I really like the concept, but it seems it hasn't been updated or maintained. Does anyone have any suggestions for alternatives or replacements for controlling keyframes and/or layers in staggers or sequences?

After having used After Effects for a while I have grown to greatly appreciate the usefulness of some particular scripts. Something to realize is that you need not have experience in writing scripts but rather just to know how to get AE to recognize them. All that really entails is dropping a script file into your script folder from the application menu. Anyhow, that will be described when you download them. Some will create a handy little UI from within AE via the bottom of the window menu or others you will run from file/scripts.

That said...here's the site that I grab most of mine and here are some of my favorites. Most are free, though I have purchased some. Also, you may notice a price when you look one up. That is often a suggested amount.

www.aescripts.com

1) Animation Patterns http://aescripts.com/animationpatterns/

This one is great for making common keyframe tweens like bouncing or springy-ness and what not. Make sure you watch the tutorial on that one because it has a good amount of power and customization. I'm sure that hand animating stuff is often a good route but sometimes that can be harder than you want it to be and you just want sliding text to have a little extra something, etc.

2)Compose Geek http://aescripts.com/pre-compose-geek/

Now, I haven't used Compose Geek but I used what looks like the inferior and free one called pre-compose.
http://aescripts.com/rd-pre-compose/

What these scripts do is GREATLY increase the ease of making pre-comps. Now, you know when you create a pre-comp now, with say 5 layers and the precomp becomes the ENTIRE goddamn length of the parent comp? So annoying. These prevent stuff like that. Well worth a look. Compose Geek looks like it will make working between Premiere and AE a lot easier.

3) Rift http://aescripts.com/rift/

Oh man, don't you hate when you have a lot of layers that you want to just stagger by a few frames? Or maybe randomize a ton of layers? Rift is for you. Turn minutes into seconds.

4) Copy to mask http://aescripts.com/copymask2layer/

Oh man. This is probably going to be one that now that you know exists makes you want to go back in time and deliver it to some pissed of past version of yourself. Have you ever made a mask on a layer only to realize that the layer was shifted all weird or whatever? And then you past that mask onto another layer and gets positioned all weird and then you have to hand position it? Oh god...but maybe you had a bunch of keyframes on the path? Copy to mask fixes that problem and pastes it exactly how you want it. This one saved my ass more than once.

5) True Comp Duplicator http://aescripts.com/true-comp-duplicator/

Alright, here is another one that is a serious life saver. So, say you have a complicated comp, full of ton of other comps,etc etc. Well, this lets you make a duplicate of a comp and it makes duplicates of all the children comps within it. if you manually duplicate a comp in your library all the children comp are NOT duplicated. So, lets say you have comp A which contains within it comp B. You make a dupe of comp A and now you have A2. Well, that A2 still has B inside it. If you altered B it would also effect the B inside A...well, because it's the same comp. True comp eliminates that. It goes and duplicates EVERYTHING. Trust me...you will someday want this if you haven't already.

6) Magnum the edit detector http://aescripts.com/magnum-the-edit-detector/

Ok, I've never used this one but I put it in here to blow your minds. I didn't even realize scripts could do this sort of thing until I saw this one. It is able to detect edits inside of a single video clip and spit it into separate layers or comps, etc. That is just cool. I've never had a use for it yet but I know it's out there if I ever do.

I'll post more if/when I think of them!