There are a lot of OBDII options, both software and hardware based that exist. I'm going to list the websites and software applications I myself have purchased and/or would purchase if I were looking for a solution. This list is also composed only of manufacturers of the software or harware themselves, not the resellers. You can buy direct from any of the sites listed below.
If I had to group up the hardware that was out there, the more popular solutions available today, I would place ELM at #1 (although I do not think it is the greatest interface, it is one of the most, if not the most popular ~ one of the cheapest solutions available). Secondly, you have your ELM emulated devices. Devices that were developed to act like ELM, but do not necessarily run with the real ELM chips, often offering a faster interface in exchange. Next you have other open devices such as the mOByDic and Mongoose (supports the J2534 standard) ~ these devices run much faster and in the Mongoose's case, costing a premium for the hardware, but like the ELM have various software support. Finally you have what I would refer to as proprietery or locked devices. These devices are not as well known because they are usually tied to one specific type of software, such as the ones you would find in AutoTap or AutoEnginuity. The packages are usually a little pricier and you are stuck with what you buy, but the packages, imo are usually a little better and offer more enhanced functionality then you would find in the general market.
(in alphabetical order)
ELM based interfaces (the real chips):
ELM Supported Software:
Mongoose Hardware (J2534):
J2534 Supported Software:
Joel's Top Package Picks:
Further OBDII Information (definitely worth the read):
Other OBDII websites:
If you stick to the list I think you will be satisfied with the results, regardless of which direction you decide to go. I have talked with the owners/developers of every site I have listed ~ some I know better then others, but I am confident each seller here would offer you a good product and provide good support to follow up with on the sale.
It is also worth mentioning that StreetDeck also has OBDII support if you are looking for a media solution and a side order of OBDII.