Actually, IMHO, I think even an "I'll have" or "I want" is fine, if it's delivered in a pleasant tone, along with a smile or a "please" or "thank you."
"I'll take the prime rib, please; medium rare, potato loaded. Thanks!"
"Let me have the fish. Oh, and would you mind asking them to leave off the green beans? I'd appreciate it."
I think that's perfectly okay. It's the "Gimme salmon!" crowd that's being rude.
Bear in mind, however, that I tend to thank servers automatically, even if they're just filling up my water glass. That, and the good tips, probably explains why I tend to get such good service so often...