Best of the bunch: http://www.samsung-omnia.org/
There's a wealth of information on the Samsung Omnia and if you've arrived here via a google search, you're well on your way to incredibly useful about your Samsung Omnia.
Omnia owners most often ask a variation of the questions below:
Where's the manual?
How do I update the custom/official firmware?
Can't seem to get wifi/front-camera/3G/GPS working.
Music or calls are too soft, how can I increase speaker volume?
Google searches provide a ton of information on the Omnia and how to customize it. To sort out the good from the bad, be sure to avoid terms such as "reviews", "previews", "unboxing", "comparisons", by simply googling "Samsung Omnia" with "-reviews", "-previews", "-unboxing", "-comparisons", and or nonsense "-nonsense". The more specific your search terms like "DXHK2" (a recent firmware build), the more likely to get better search results.
There are a number of forums with incredibly industrious Omnia owners just waiting to answer your questions. The communities there are very strong. A couple of examples include: Modaco, Low Yat Net, and PPCSG. Facebook, in fact has a strong Omnia community, where the majority of users seems to be from the United Kingdom, and users seem to invite questions from new owners. Samsung also chimes in on the discussion board from time to time, evening announcing their plans to release the North American (CDMA) versions of the Omnia on their facebook fan page.
However, forums and internet searches for the Samsunng Omnia bears a lot of information that likely will either be too esoteric or very unorganized. The resources featured below, on the other hand, are well-organized, community-centred, and very timely as well.
My Samsung Omnia (Wordpress):
Very well documented information regarding customization of the Samsung Omina. Maks Pain (if that's his real name) has gone through all the tough work of reading several pages and threads of forums and summarizes all the information succintly. To get started, especially if you're just purchased the Samsung Omnia, see these articles:
Pimp Your Omnia--Info on changing the default today screen theme via SPB Mobile Shell
Omnia Tips and Resolved Issues (Info Gleaned from forums), download PDF here.
Bespoke Wallpaper for WQVGA Samsung Omnia Screen