[Janteh]

You can also use shift-option-cmd-v to directly paste without markup :)

[natch]

I can never remember which combination that is, but thanks.

[jmreid]

You can override any key combination using the Keyboard preferences.

Just make a new shortcut under the All Applications group named exactly the same as the one you want to replace. http://i.imgur.com/JqBncTy.png

I've also had to add an entry for "Paste as Quotation" because that's Mail's default use of Command-V.