I really like parallel effects. TH2/TH3 has two parallel paths, but the FX Rack itself can't handle parallel effects. The go-to for most people is Blue Cat's PatchWork, which for $99 is a great solution.
 
However I'm a big fan of the Line 6 Helix, so I was really happy when they came out with a native version - especially because it has four parallel paths, so now I can get four parallel effects in a SONAR track. Although you're of course limited to using the Line 6 effects, there's a wide array to choose from that are good for more than just guitar...and some of them have no equivalent from other manufacturers.
 
The downside is it's $400, so you have to weigh whether an open-ended parallel system like PatchWork is more cost-effective. And of course if you don't want to spend anything, you can always set up multiple buses or use Aux tracks with folders. But I'm finding that "multibanding" the Helix amps gives me the best amp simulations yet, and I also use the non-guitar FX on vocals. If this sounds interesting, you can download a 15-day trial version of Helix Native and check it out.

I tried the demo and found it to be very nice. Unfortunately I have a lot of guitar sims on-hand already. I can't justify the expense for the extra things it might do. I liked the interface because I could deep dive into a patch easily. They also give you a ton of stuff to work with. The sound quality is good, but I don't think it's dramatically better than some of the other popular sims.

I've been kind of interested, I can get it for $349 since I own Pod Farm (not a super-generous discount). I've mostly been using Guitar Rig 5, which I think sounds better than Pod Farm. I also own some of the Line 6 Model Packs though, which add some more esoteric amps and fx, whereas Guitar Rig is more like all the usual suspects.
 
How do you think Helix sounds in comparison to Pod Farm? I've tried the Positive Grid demos too, and thought they sounded really good, but their offerings are a bit confusing, and the website is a little unclear and lacks some details.

ampfixer
The sound quality is good, but I don't think it's dramatically better than some of the other popular sims.

Out of the box, I agree. But with the parallel paths, being able to do four-band distortion takes it to a whole other level. I did multiband presets for each of the amps, and the difference is significant.
 
You can do multiband presets in Guitar Rig, although using all those splits can get messy. You can in SONAR, too, using multiband compression as a crossover. But the single plug-in interface makes the process much faster.
 
Lately I've also experimented with using different amps and cabinets in the parallel paths instead of "multibanding" a particular amp, as well as using different amounts of Drive in each band, etc. I've also found that moving a slider on the graphic EQ sending lows to the lowest band can give more of an open-back sound. However for me it's not just about guitar, parallel processing for vocals is yielding some unexpected surprises.

Amplitube 3 allows for two parrallel paths...

I've used it a number of times for various effects/situations...

...and the free statup price makes it easy to get started, then add additional amps/fx/etc whenever you chose.

I believe Amplitube 4 allows this as well, but I'm not certain...

Another one worth looking at is Hofa System 2 which is limited to its own effects but has options for parallel processing. You can route anything to anything it seems by dragging and dropping modules into the window.

Keni
Amplitube 3 allows for two parrallel paths...

I believe Amplitube 4 allows this as well, but I'm not certain...

Yes, Amplitube allows for two parallel paths. The CA-X Biamp Power Chord amp uses TH3's parallel paths. However for multiband processing with amps, two bands doesn't really cut it because you can do only lows and highs. Four bands allows for a lot more definition. Cubase comes with a virtualization of the Quadrafuzz, the four-band multiband distortion I designed back in the early 80s, and iZotope Trash allows for multiband distortion as well. But what appeals to me about the Helix is that it allows multiband processing that's not only distortion.
 
 

another option is ddmf's metaplugin https://ddmf.eu/metaplugin-chainer-vst-au-rtas-aax-wrapper/

I thought I knew what "parallel effects" was but, having read the above I'm not so sure.

Can't you just put each effect on a buss an use sends?

synkrotron
I thought I knew what "parallel effects" was but, having read the above I'm not so sure.

Can't you just put each effect on a buss an use sends?

Yes or aux tracks.