Hi dralanir,
I would endorse The hatter's and Grant's recommendation of the OWC Mercury Extreme Pro range of SSDs as the best choice for your new Mac Pro, and would advise against buying an OCZ SSD.
Having both an OCZ Vertex EX 60GB SSD, and an OCW Mercury Extreme Pro RE 100GB SSD myself, there is one major, and very significant difference between the two companies. OCW is a very Mac-friendly and Mac-orientated company, whereas OCZ most definitely is not!! OCZ do not want to know unless you use Windows, and there is no way that I want, or need, anything other than the Mac OS on my system. "Dimdows" is banned!!!
I imported my OWC SSD to the UK from the USA, in preference to buying another OCZ SSD from a UK reseller, and I have not regretted that decision.
You do not need an adaptor for a 2.5" SSD if you install it in the Mac Pro's lower optical drive bay, and, in my opinion, unless you need two internal optical drives, that is the best place. It is extremely easy to install an SSD in the lower optical drive bay of a 2009 or 2010 Mac Pro:
http://macperformanceguide.com/Mac-InstallingSSD.html
Installing your SSD there leaves your Mac Pro's hard drive bays free for future expansion, and I use mine for a 4 drive striped RAID 0 of WD VelociRaptors. My SSDs are used only as system boot drives (OS and applications).
Regards,
Bill