The Saddlebred seems to cross well with most breeds, if attention is paid to the actual animals being bred (to avoid glaring conformation issues). It really depends what you want to do with the resulting foal - the Saddlebred itself has been a real "jack of all trades" throughout it's history.... From cavalry horses, to carriage horses, to farm horses, to pleasure horses, to plantation horses, to stock horses, to jumpers and dressage - almost every one I have met has a strong desire to be with people. They often add refinement and flash to whatever they are bred to.
Some of the most smashing sporthorses I have seen recently are between 1/4 and 1/2 Saddlebred with the remaining being European Warmblood.
I also love the Shire or Clydesdale crosses... Personally I am not a huge fan of the Friesian/ASB - I, personally, find them just too upright and upright moving, generally speaking, though I have seen some very nice ones so I can't deny that the right individuals make a big difference.
Arabs make for a nice cross... And I have seen some real drool worthy Standardbred(trotters) and Morgan crosses too (going back to their roots a bit).
And of course, I also like the purebreds... Especially the larger boned "old style".
This is our 2012 Saddlebred/Clydesdale cross (he's still shedding some coat, which he got gummed up rolling in something that just won't come out :( )