Hello Alex:
Depending how cheap and ghetto you want to get, there's also possibility of doing WDM on 1310/1300. I have custom-manufactured splitters filtering 1307nm +-2nm - and any given LR XFP [*1] will be either within that band or outside [*2]. Test a bunch of them, split them into two groups, use on the "tested" wavelength. Bunch of friends&family are using this technology in production. This gives you an ability to do 20G with very cheap optics.
[*1] Except ones with very temperature dependent wavelength - mark them as "warms up to 1300" and use if you don't care that your links will take about 5 minutes to "warm up" and come up. :)
[*2] Any LX4 Xenpak would be "outside" of the band as well, and you can use LX4 concurrently with LR.
There are some more ghetto fabulous things you can do, described in http://www.nanog.org/mtg-0610/presenter-pdfs/pilosov.pdf ;)
-alex
Do you have any issues with four wave mixing or other crosstalk issues or do you account for this in your channel plan? Regards, Mike