Let's see from what I've heard myself.

Apex'i WS-4cyl Deep and Onry, although quite a bit loud at higher RPMs, 6cyl Mean as all hell, very deep and grumbly, but again still pretty loud at highway speeds as with most catbacks

5zigen Fireballs - 4cyl axle back: Very Deep, Great tone, fairly quiet at highway speeds, 4cyl with custom catback, holy mother of god loud, but very very onry sounding, nice and deep, but did I mention loud? 6cyl axleback, fantasic low end sound, super super deep and grumbly, sound cuts out a little too soon, and it's quiet at a moust by v-tec(3800rpm for me), although from what I'm told there's a very defined pop at higher rpms. 6cyl custom catback with no resontators at all and a test pipe(no cat)..I wouldn't wish these on my worst enemy, great for a 5 minute rip down the cruise, but way way too loud.

Magnaflow 4cyl custom catback with racing cat, great tone, nice range, a tad noisy still at highway speeds, but some folks like that. 6cyl custom catback, deeper than the 4 but same characteristics.

DC Sports Catback 4cyl Fantastic Sound, very very deep, but again as with most catback a bit noisy for my taste at highway speeds

Comptech sport- 4cyl with custom catback and 1 resonator left, very very deep, but very very noisy, 6cyl axleback deepest tone I've heard from an accord, but very quiet.

Greddy Evo 4cy catback, sounds like a heard of bees in a tin can, and that thing has like a 10" can

HKS Super Dragger for 5th gen 4cyl, again heard of bees in a tin can and my god what a huge can

Tanabe Super Medallion, 4cyl catback, Nice looking, good sound, pretty quiet at highway speeds, but you know it's there when you pounce on the gas. 6cyl catback, NIIIIIICE sound..

That's about all I've heard that I know of. I like my fireballs on my v6 and I like how it sounds with just an axleback on the 4cyl, but the fireball with custom catback(just used the universal fireball) was way to onry for me, the 5zigen catback is pretty nice sounding and the cans aren't too big, I've heard quite a few magnaflow setups on 4 and 6 cyl and I like how they sound albeit a bit noisy on the highway. I'd drive around a while and try your hardest to notice folks exhausts, when you hear one you like ask them what it is.

For me, the next exhaust will be comptech, I like my fireballs, I just don't like how they hang.