OK, this is going to sound odd, but I have a reason for my madness.... I posted this on a couple of other forums, and Morgan (Leafgurl) suggested I ask the super knowledeable people here :D

If you were to take a nice solid royal blue like this: http://www.aquabid.com/cgi-bin/auction/clo...tashm1210212997

or this: http://www.aquabid.com/cgi-bin/auction/clo...tashm1210951922

and cross it with a red, yellow or black female, which cross is most likely to give more blues?

All the info on genetics that I can find talk about the blue trait (Bl/bl) by itself, but never talks about what the Bl/bl genotype is in red, black or yellow fish. Is the Bl/bl completely absent in these other colors? ie: is there a Bl- or bl- gene as well as the Bl and bl?

I'm guessing that the red x blue would give either multi-colors or blue with red wash, so it's probably not a good choice. But, how do the yellow and black inter-react with the blue?

I'm pretty much figuring on running such a cross for several generations so ideas on what might be possible with F1 crosses and F2 crosses are appreciated too.

No pics, but I would guess red/blue and yellow/blue are both going to give you blue/red multis and blue with red wash, possibly some red with blue irrids as well..
This is going on the assumption that the blue is not carrying yellow, or NR1, to be precise. If the blue is carrying yellow then I would expect blue/yellow multi's and blue with yellow wash.
Blue bald black is going to give you blue and black fish, probably lace. I think this is the most likely combination, but it depends on the genetic make up of the black fish as well as the blue fish.
You would probably see better long term results using a black lack/back copper, even a melano cross to blue, and breeding for blue show wise, then you would crossing into reds or NRs. Though breeding to red or NR1 would give you blues faster, they would not be show quality blues.
By the way, the links were broken for me.

Sorry about the links Bella, here is the first one again...

http://www.aquabid.com/cgi-bin/auction/clo...tashm1210212997

The second is much the same but a "brighter" blue and not nearly a nice finnage.

To be honest, the color that I am considering working toward is a true blue dragon. I have some nice dragon genetics to work with here (red, yellow and black, as well as red/green) and thought it might be fun to work towards a blue (something I haven't seen yet on AB). I figured it would take at least 3-4 generations alone to get anything half decent with the dragon coloration since the initial cross would be dragon x non-dragon. Although, if I can obtain a good metallic blue like the one above then it might help.

Well, I have to say this.. Half pf everything is about the picture.
I can almost promise you that fish doesn't look like that in real life. The reason I say that, is because they took very low light pictures of the fish, to give him a matte color with his blue.
If you hit a light on him, he would probably be less an even color blue, though that IS a beautiful royal.
I honestly think the BEST way to go with with blue marble, and there is a reason..
First most marbles carry red loss. second, you will, if you care luck, be able to show in three classes, solid, marble and BF. Third, you'll get a cleaner blue with marble then you would with any of the other color choices.
But going different ways and trying different things is the halmark of a good breeder. Don't be afraid to break convention and to your own thang. If that chapter is missing in the betta book, then write it yourself.

Nicely said Bella! ;)

LaBella, I know what you mean with the marbles - I had a really nice blue marble who became solid shortly after I got him and his color was suberb. So, with that in mind, I see that Rung has a few new boys on AB (that was who the afore-mentioned blue marble was from)....

This fellow reminds me a bit of my old marble, except that Rainy was a royal rather than a steel: http://www.aquabid.com/cgi-bin/auction/auc...ashm&1213283362

This fellow is the color blue I'd ultimately like to achieve - knowing that it's a partially dominant combination - and he is a beautiful royal as well. I suspect he probalbly carries the marble trait - I'd bet the two are spawn siblings!
http://www.aquabid.com/cgi-bin/auction/auc...ashm&1213283362

I'm thinking it might be useful to start the line with the Blbl rather than the blbl in order to ensure that both genes are present in the line somewhere. What do you think?