Tutorials of utmost importance. Read these before you do anything if you're a total noob, or even if you're not, read them.
Code
http://www.deviantart.com/download/55042010/Full_Signature_Tutorial_by_Senthrax.jpg
http://www.deviantart.com/download/89049660/Lighting_Tutorial_by_Xpnze.jpg
http://www.deviantart.com/download/62834863/_Vision__s_text_tut_by_TheFriendlyGuy.png
http://www.deviantart.com/download/90551186/Typography_Tutorial_by_Xpnze.jpg
3 parts to this one.
http://img808.imageshack.us/img808/4566/compositiontutorialpart.png
http://img130.imageshack.us/img130/4566/compositiontutorialpart.png
http://img683.imageshack.us/img683/4566/compositiontutorialpart.png
General sig making tutorials. This will help you learn new techniques and how things come together.
Code
http://img96.imageshack.us/img96/8596/tuttut.png
http://img855.imageshack.us/img855/5426/linktutorial.png
http://sanderrednas.deviantart.com/art/signature-tutorial-70881138
http://sh-archaeologist.deviantart.com/art/Music-Man-Signature-Tutorial-70326440
http://fc09.deviantart.net/fs42/f/2009/106/c/9/Advanced_Signature_Tutorial_by_Reflectionartwork.jpg
Stocks.
C4D packs.
Code
http://lordsiyei.deviantart.com/art/C4D-Effect-Pack-77148538?q=boost
http://rosecabriolet.deviantart.com/art/Pack-c4d-effect-bubbles-128526593
http://narutobigit.deviantart.com/art/C4D-Effect-Pack-1-139092774
http://simplegfx.deviantart.com/art/SO-C4D-Bubble-Pack-1-187750308
http://iaminnovation.deviantart.com/art/C4D-Pack-No-1-92362888
http://00chaos8.deviantart.com/art/c4d-Supreme-Pack-32-Renders-89849547
http://oldmanjames.deviantart.com/art/Final-Render-Pack-28900717
Other stocks.
Code
http://jotodal.deviantart.com/art/Stock-Pack-74557139
http://www.megaupload.com/?d=UQ3IV7VO
http://shakethelife.deviantart.com/art/HQ-Stock-Pack-133943714
http://kire1987.deviantart.com/art/Nebula-Resource-Pack-95045980
http://kuschelirmel-stock.deviantart.com/art/Textures-02-Stock-Pack-93685535
PSD Packs. Remember these are LRO (Learning rights only), so don't use the sigs that they've made.
Code
http://lahabz.deviantart.com/art/PSD-SigS-PaCK-2-175225686
http://luquicas.deviantart.com/art/Another-psd-pack-158527108
http://ezekdesigns.deviantart.com/art/MegaPack-Psd-s-LRO-157136903
http://jphilly.deviantart.com/art/JPhilly-PSD-Pack-2-122436495
http://shando91.deviantart.com/art/psd-pack-n1-Easyway-134349836
A few tips.
Use high quality stocks. Stocks can make or break a sig.
Get Topaz Vivacity. It can be really good when used appropriately, it can also ruin a tag when overused/used inappropriately.
Apply Image (Shortcut: Ctrl + alt + shift + E) and use Smart sharpen/unsharp mask at the end of making a tag. Add borders AFTER this step if you're planning on using a border. Smart sharpen/unsharp mask are also great to use on your focal stock when you start making a sig, can make quite a bit of difference.