For several years Ken Nordtvedt has been sorting Y-DNA haplogroup I into different groups based on patterns in STR marker values (these are the "37 markers" etc. reported by genealogical DNA testing companies like Family Tree DNA, SMGF, Ancestry.com). These patterns can be found in Ken's FounderHaps.xls Excel file at his website http://knordtvedt.home.bresnan.net/. If you don't use Excel, this website gives the patterns ("modals") in "Family Tree DNA order": http://dgmweb.net/genealogy/DNA/Hg-I-subclades-FTDNA-order.shtml
(You can click on the links to go to the websites, and you can click on my tree to enlarge it).
Although Ken was able to use his modals to distinguish several groups within haplogroup I2a, (he called the largest groups Dinaric, Sardinian, Isles and Western), most of these groups did not have a SNP to identify them. And without an SNP, many scientists, genealogy testing companies etc. did not accept these groups as proven.
In 2009 and 2010, four members of the I2a project at FTDNA did a "Walk on the Y" to sequence a portion of their Y chromosomes and 6 new SNPs were discovered. Some of these seem to be equivalent to previously known SNPs (L158 and L159.1 are equivalent to M26, and L178 is equivalent to M423. The new L161 SNP confirms Ken's modals: his Isles group tests L161+ while his Dinaric and Disles groups (and all the rest of I2a) test L161-.
But there are two new SNPs which showed us new things which weren't predicted by Ken: The new SNP called L233 separates Ken's old I2a*-Western group from I2a*-F and all the rest of I2a: Western and Western-Isles all test L233+, while I2a*-F and Dinaric, Sardinian, Isles and Disles all test L233-. This much was expected based on Ken's work. What wasn't expected was that a very small number people who he had placed in Western tested L233-. Closer inspection showed that they had slightly different 37 marker results from most Western, and a new group was found, which Ken called I2a*-Alpine because the few known members come from southwestern Germany, northeastern Italy, and Romania.
On my latest I2a tree shown here I am including I2a*-Alpine for the first time. You can see a previous version of the tree here: http://cullengene.blogspot.com/2009/12/tree-of-y-dna-haplogroup-i2a.html at that time we had not tested enough supposed "Westerns" and hadn't learned of the "Alpine" group yet.
The other very interesting new SNP discovered in the WTY is L160. Some of Ken's Sardinian group test L160+ and some test L160- and it can't be easily predicted from 37 or 67 markers. That is why I show the green I2a1a and I2a1a* triangles as overlapping, since their modals/marker values overlap a bit.
As of August 26, 2010 the ISOGG tree includes all SNPs shown here, and hopefully commercial DNA testing companies like Family Tree DNA and 23andMe will update their trees soon. You can see the most recent ISOGG tree at http://isogg.org/tree/ISOGG_HapgrpI.html , and the current offical FTDNA tree at http://www.familytreedna.com/snps-r-us.aspx, and the working draft tree of Dr. Thomas Krahn at FTDNA at http://ytree.ftdna.com/ (use the drop-down box at top to switch between his draft tree and the 2008 YCC tree which is the oldest tree of all of these).