Handsome John, if Dany cannot bear children, then yes she'll need a surrogate to bear an heir to continue her dynasty...
I think we'd all agree that there may be two other Targaryens or half-Targaryens males out there... Aegon and Jon. But are there any females? My craziest theory says yes... Cersei. (I won't go into it here, but the theory says Cersei, Jaime, and Tyrion are all Dany's half-siblings.) But I doubt Cersei will live long enough to win Dany to her side...
So that means a non-Targaryen princess will marry Dany's Targaryen (or half-Targaryen) husband. Since I think that most of us think this will be Jon, current events at the Wall not withstanding, then Jon will need a fruitful girl to bear children... Since Dany cannot fail in this (she has no other siblings, uncles, or cousins to inherit after her), she and Jon/Aegon must have a princess that will bear children. Remember how Jon Arryn wanted a bride that he knew was capable of bearing children? Well, I think Dany will want the same. At first glance, this may put Cersei at the top of the list... But Dany will also need a strong political alliance with this marriage... so Cersei is out. Arianne could be a candidate as Dany's first cousin, but she's not proven herself to be fertile. Sansa is also a tempting choice in order to secure Baelish's loyalties, i.e. the Vale and the Riverlands and the North, but she's not yet shown she can bear children... but Jon may like this choice since he's got a serious Jones for redheads. (It's not totally gross, I mean Jon is probably more closely related to Dany than Sansa.)
But if Dany is looking for a political alliance to a great house with a princess who's known to be fertile then Asha Greyjoy, Margaery Tyrell, and Jeyne Westerling are her choices.
Yes, Margaery has been married to three consecutive Baratheons, but the Tyrells used to be stauch Targ loyalists. Mace, Olenna, and the family may smell the roses and avoid getting pruned by allying with the Targs. Plus, Pycelle has been giving Margaery moontea. If you're asking why, then slap yourself and then go pour yourself a whiskey to catch up with me.
Asha Greyjoy. If I remember correctly, didn't Asha think she was pregnant once? She's also the niece of Euron.
And finally there is plain Jeyne. Catelyn noted right away that Jeyne had great hips for birthing. Jeyne was actually noted to be pregnant with Robb's son. And politically speaking, Jeyne could help bring back the Westerlands to the Iron Throne while also bringing in the loyalty of the Stark supporters in the Riverlands and the North.
But mayhaps the curphecy (half curse, half prophecy... by the way I just made that up) simply means that Dany will name her child Drogo... i.e. "After you name your son Drogo, then he'll be returned to you." I am so smart. S, M, R, T.
Edit: Beta posted before I finished mine...
Beta, I personally want to congratulate you on seeing the possiblities of Aerys II and his penchant for taking what was not his. Now, I'll launch into A+L=J. We know Aerys raped his own wife and Dany was conceived. We also know Aerys loved/lusted after Joanna Lannister. We all know Cersei and Jaime have almost platinum blonde/golden hair. We know that Tywin resigned as Hand. We all know Lyanna disappeared from court and Rhaegar was blamed. We know that Brandon demanded justice, but Rhaegar was nowhere to be found. Robert says Rhaegar raped Lyanna, but everyone else claims that Rhaegar was honorable to the very core of his being. We also know that Rhaegar was already married and that abducting Lyanna or even eloping with her could easily cause a rebellion by the Starks, if not the Martells as well.
I think Aerys asked Tywin (only twenty at the time) to be be Hand because Aerys lusted after Joanna. He'd often send Tywin out on business and then Aerys would seduce/rape Joanna. Knowing that Tywin would rebel and that the Lannisters would be annihilated, Joanna kept her silence. After the Defiance of Duskendale, Aerys' paranoia and megalomania grew and he became a serial rapist. The Kingsguard overlooked all this. Lyanna caught Rhaegar's attention with her sense of justice and her courage. She also caught Aerys' eye and he took her by force once they got back to King's Landing. Lyanna was not as easily cowed as Joanna and she told Rhaegar. Rhaegar smuggled Lyanna to the safest place he knew, the Tower of Joy. But before he could get back to KL and confront his father, the Arryns, Baratheons, Starks, and Tullys had risen in revolt. Rhaegar was faced with the choice of confronting his father which would have divided the Targaryens and probably ended with all their deaths or putting down the rebellion and using his new power and glory to force Aerys to abdicate. Rhaegar chose the latter and died.
Handsome John, did you ever see the movie The Italian Job? Despite having Donald Sutherland, Edward Norton, and Charlize Theron... it's very average. But the scene where Jason Statham (playing the character Handsome Bob) seduces the cable girl is brilliant. It is the best seduction scene.... ever. Ever.