Wrote myself a Garen guide on Mobafire (yeah, I know), and it's been getting people fairly decent success. It's nothing gimmicky, it's nothing bold, but it has a lot of detail about playstyle and thought processes and strategy as opposed to just an item build telling you to get snowball items and then telling you that you should dominate easily.
Dominate how, right? My guide is pretty thorough, and even if you don't have an account at the site, you can leave feedback here.
The Scoundrel Will Pay: A Guide to the Effective Garen
The short version:
You need to build both survivability and damage. Building straight tank Garen will leave you useless, and you're only going to be useful for stealing kills with your ult and a short duration silence. Building straight damage means you're going to get focused down and everybody knows that your DPS when dead is zero. You need to find that golden mean between health and damage and build straight into that.
Your core of items is:
And trust me, it works. Your movement speed is important, and if you're not getting Boots 3, you need to get Mercury Treads (since your movement speed while stunned is zero, and that's not good.) Frozen Mallet lets you get a good slow off every time you hit with your Q, which should be a lot.
Start with Q.
And then whatever.
Get more Q if your enemies are moving faster, get more W if you're getting killed before you're done spinning. Get more E if you're moving fast and living through their pitiful damage already.
The rest of the information is in the guide. It's not a hard read. ;)