There is no default key binding for this; however see pjammer’s answer — list-processes+ includes (among other things) a kill binding on C-k — and also Joao Tavora’s answer — which provides just a kill binding (for the same key).
event_jr points out in the comments that you can use M-: (kill-process) RET to kill the current buffer’s process.
More generally: You can use M-: (kill-process PROCESS) RET, where PROCESS “may be a process, a buffer, or the name of a process or buffer”, with those names being as they appear in the output of list-processes. Process names take precedence over buffer names, should you happen to have a conflict; so it’s probably best to be in the habit of supplying the process name.
Alternatively, Emacs 23+ has a general system process manager (M-x proced) which is more akin to running top, and which does have a default binding for sending (arbitrary) signals (k). Of course it may be far less obvious in that listing which process you’re interested in.
Edit: Better late than never 🙂 The following enables M-x kill-process RET to be used (tested in Emacs 26.1):
;; Enable M-x kill-process (to kill the current buffer's process).
(put 'kill-process 'interactive-form
'(interactive
(let ((proc (get-buffer-process (current-buffer))))
(if (process-live-p proc)
(unless (yes-or-no-p (format "Kill %S? " proc))
(error "Process not killed"))
(error (format "Buffer %s has no process" (buffer-name))))
nil)))