Woohoo...I'm a mod, I get to answer this one:

I hate to say it, but in car audio, for the most part...wire is wire.

There are some subtle differences, but when shopping for wire I would look at the following:

RCA:
Find a good solid connector on the end...gold plated. Metal barrel. Some type of strain relief is good as well. Make sure it's a twisted pair. This does help in the noise reduction qualities of the wire. Again, most of these companies are putting out the same damn things with different pretty colors on them, and jack the prices way, way up....again, this is just my personal experience. Some people say that they can hear the difference between cables....if you can it's certainly up to you. I've used Stinger, PG, RF, LA and a few other cables in the past, and I've never felt that any provided sub standard performance

Speaker wire:
This is another bone of contention...again with the noise floor that exists in car audio, I don't think that you will find any real differences. The RF/IXOS Gamma wire was a design that is commonly employed in home audio DIY cables. You can make some extremely high end speaker cable out of Cat5 cables if you really want to try it. Thesecables are heralded by a bunch of wire gurus....check out the wire section at www.audioasylum.com Personally I think some of it's smoke and mirrors. If you system doesn't have the resolution to distinguish between two types of cables, then do you need the expensive stuff? Probably not. Just make sure it's properly sized. I HATED the PG ZeroPoint wire...sure it looks cool, but it's a pain to strip and worse to run in a car, it's very thick...between 4 and 8 ga.

Power wire:
Again mostly cosmetics. This is the most important cable you will run...make sure you do it carefully and safely!! FUSE it people....no more the 18" from the battery. Protect from all sharp and moving objects....it can burn your car down...so can a remote wire, so disconnect the battery and pull all fuses before moving equipment...why do I stress this...because I almost burnt a car down from not doing it....learn from my mistakes!!

Make sure you get these things sized correctly. A 4 ga wire at a run of aruond 12 - 15 feet long is good for around 100A if memory serves me correctly. It may be a bit more, a bit less. I'll try to post a few tables later. It may cost more to upgrade, but skimping here will cost you down the line.

Again, there are lots of pretty colors out there to choose from. You won't find any performance benefit from using platinum plating, square wires, etc. The only think you should look for is strand count...the higher the more flexible, the better. Also, make sure the line you choose has what you need....Stinger is probably the most comprehensive lineup out there...they have EVERYTHING...I like this brand...lots.

The BEST wire out there.....without looking at money that is specifically made for car audio...I'd say in the power delivery realm, you are looking at XIOS. Thier GTI line is extrememly versatile and configurable. The inputs and outputs on their fuse blocks are modules, so it can change and expand with your system. They offer that cool new square wire, and they also use Mini ATC fuses that are configurable to give you fusing on a single line from anywhere between around 3 and 560A!!! Talk about designed for you. It's really an excellent line...but you pay for it..retail on the GTI 0ga kit is around $700..no that is not a typo.

The best signal cable out there...probably Kimber...again we are talking 10000 for a few feet of wire...high end stuff. Personally I don't think that it's nearly worth the money for this kind of gear.

What will I be using....I hand build my cables for home and car audio use now. I use mic cable and some generic RCA/XLR connectors for interconnects

For power, I really like Stinger...even their basic proseries stuff is nice. PG made a really nice piece that controls not only power distribution but also your amp remotes for a ton of different pieces of equipment...check it out at www.phoenixgold.com Pretty slick gear - but expensive.

Darvex.com does have good pricing, but I have found that Knukonceptz.com has the best bang for the buck out there...I hope you like blue though...that's all they come in. I have not used this wire personally, but I have heard enough testimonials....it's worth the money.

Will you need sounddeadening.....
Personally, I think that sounddeadening is an integral part of ANY installation. At the least, do your doors...you'd be surprised how nice it is to hear your doors close with a thud rather then your uual "ting" Make the car feel stronger. This can always be done after the fact, but it's a PITA

I think that covers most of it.....the above is just based on my experiences.