All Sounds Need Effects.

Native Instruments Guitar Rig 2

To be honest, this program is a bit more than "an effect". It contains as many amplifier, speaker cabinet, and guitar "stomp box" simulations as you could possibly need, and throws in a guitar tuner and a couple of "tape decks" as well.

It works wonders for basses and vintage keyboard sounds, too.

ArtsAcoustic Reverb

This flexible reverb (echo to you non-technical/musical types), capable of replicating everything from normal spaces to looong, wishy-washy, wurly-swirly whooshes, features on just about every recording I do.

Kjaerhus Audio Golden Audio Channel

It's a noise gate. It's a de-esser. It's a compressor. It's an EQ. No, wait. It's two compressors. And EQs...

Anyway, there's not a single audio recording that doesn't need at least something of what GAC has on offer, so this is another of the rare "constantly all over the place" effects plug-ins.

Kjaerhus Audio High Precision Mastering Limiter

This is one of those products that has such a boring job you almost feel silly for spending money on it. (Like mixers.) However, a good mastering limiter is crucial to the control of final dynamics and output level.

Other Effects