Not a spell checker, but you can use my Selector program to conveniently paste text in an editor with a spell checker. Yes, you can do the same thing "by hand" but Selector sits in the tray providing several types of interface between regular apps and the clipboard or selected text.
You may download Selector from this page:http://www.favessoft.com/hotkeys.html#Selector
As example, I select a few lines from my hotkey page, hit the hotkey for Selector window to pop up, choose PsPad from the list of apps whose shortcuts I have added to the list via drag and drop, then hit the Paste button.
The clipboard text is saved as a temp file and opened in PsPad. Press F7 to spell check.
I'm sure you can find dedicated clipboard based spelling tools. Selector is for various tasks that kind of fall through the cracks. Such as opening the url in the address bar of a browser in a different browser without using a plugin. Launching any app with selected text as command line param etc..