Besides “Bitcoin: A Peer-to-Peer Electronic Cash System”, which is more like a brief description of the general framework, are there other ‘scientific or research grade’ studies about Bitcoin technology? Can similar decentralized crypto-currency models be found in the literature?
Bitcoin is a relatively new phenomenon and the peer-review process takes a while, so there is not much out there yet.
The most notable is a network analysis of bitcoin transactions done around the alleged "allinvain" theft earlier this year.
Other than that, there are currently a few articles published in academic journals that focus on bitcoin (as well as pop-sci and pop-compsci articles in various places)
Grinberg, Reuben, Bitcoin: An Innovative Alternative Digital Currency (April 21, 2011). Available at SSRN: http://ssrn.com/abstract=1817857
The best answer may be to do this in the form of a community wiki where articles published in academic journals can be posted by subject, as if bitcoin survives it will obviously start to receive a lot of attention.
Yes, there are studies about decentralized digital currencies. Some of them use ideas very similar to what Bitcoin chose, for instance refer to chapter 2 of this thesis. The following Google scholar serarches will give you more reading:
The basic premise of a decentralized mint is not a new idea, and has been studied for a while.
Let's group all the answers in this Wiki. Suggestions shall be provided in new answers, relevant (voted) ones will be included in this list, sorted by category and publication date.
Distributed currency models
-  Chapter 2 of Flavio Garcia PhD thesis: “Formal and Computational Cryptography: Protocols, Hashes and Commitments”.
- [2011, Jul] ArXiv paper by F. Reid, M. Harrigan: “An Analysis of Anonymity in the Bitcoin System”
There are some papers on Bitcoin and related topics here: - http://en.bitcoin.it/wiki/Research
I think that http://bitcoinacademic.wordpress.com could be able to help. There is a wide collection of academic research in many fields. However, you are right, there are not that many peer reviewed journal articles out there, but I do think some of this research is valuable and provides interesting insights.