Desalination. The most appropriate alternative, actually. Instead of iceberg transportation from distant latitudes, there could be build desalinating facilities around the coastal lines, and to pipe the obtained sweet water deep into the desert.
Methane. Just like the icebergs - depending on the utilization this gas could be considered as a threat - greenhouse gas, or as an advantage - energy/H2 source. 10 to the 9th tonnes of methane are flared off by oil wells each year. Anyone who has taken elementary chemistry can calculate how much water is produced in burning that amount of methane. In order to condense it out one must cool the exhaust, and the best way to do that is to evaporate sea water, which when added to the water condensed from the burnt methane gives much more than 10 to the 9th tonnes of fresh water.
Weather modification. Dispersing silver iodide in the sky through planes or rockets. The moisture from clouds forms droplets around the small particles, and this leads to raining.
DriWater. This is very progressive technology that transforms liquid water into jelly. Then certain quantity of this jelly is placed near the stem, and the roots of the plant thus securing its constant irrigation. Because of the consistence of the jelly the water is not absorbed at once, but in certain period of time, defined by density and quantity.
All these and other water delivering methods require price and ROI calculation, as well as comprehensive computer simulation. Each one of them could be considered as too expensive in one point of view and most preferable in another one. That is why perhaps the best way is to use combination between all of them, and to apply the most appropriate one in specific situations.
Here you may see few links to:
Similar purpose projects – searching different ways for watering and greening the deserts / fighting CO2:
Major international agreements on climate change:
Some of the most aware organizations, respectively most probable participants in an eventual operation: