As I predicted in "PTHPasteboard Returns, Better Late than Never" (2005-03-21), Paul Haddad's PTHPasteboard 4.0 is here, it's free, and it's better than ever. PTHPasteboard is a simple but powerful automatic multiple pasteboard: basically, every time you choose Copy or Cut in any application, PTHPasteboard remembers the clipboard contents, so that you can later paste that item even though you have subsequently tromped on the system clipboard with another Copy or Cut. With PTHPasteboard, it becomes trivially easy to collect multiple items from one place or many places and paste them separately elsewhere; unless you've experienced it, you may not realize how much easier your entire workflow becomes when suddenly there is no need to plan or hesitate before copying, because all your recently copied items are available to you, everywhere, all the time.
PTHPasteboard 4.0 is a significant rewrite. Options are now managed through a System Preferences pane. The saved clipboard items (referred to as "buffers") are accessed through a window. This window can be constantly present, or it can be manually summoned and hidden, or - this is what I use - it can appear temporarily, sliding into the screen from the side or bottom when you hover the mouse over that region (like the Dock's hiding behavior). Frequently used material can be stored in additional windows (rather like the old Scrapbook). Windows are searchable. You can learn what application a buffer was copied from, and when. Hot keys can be defined to show or hide particular windows or paste particular buffers; I find the simplest approach is to summon the window through a hot key and then type a buffer's number to paste it. (So, for example, to paste buffer 2 from the main PTHPasteboard window, I first press Shift-Option-Command-V, which shows the window; I then type "2", which pastes that buffer and hides the window.)
If you want even more power, or simply want to assuage your guilt over getting so much for free, you can pay $20 to upgrade to PTHPasteboard Pro. This adds syncing, whereby the contents of clipboard windows can be shared between machines across the local network. It also adds filtering, letting text pass through various pre-defined transformations as it is pasted. (Personally, I'd prefer a feature that lets me write my own transformations in some well-known scripting language.)
I've used various multiple-pasteboard utilities for years (see "Multiple Clipboards on Mac OS X", 2003-02-17), and my advice remains the same: you owe it to yourself to try one, and PTHPasteboard, for its clarity, its power, and its wonderful "set it and forget it" ease of use, not to mention its (lack of) price, is the one to try. PTHPasteboard 4.0 is a universal binary, and requires Mac OS X 10.4 Tiger. It's a 1.3 MB download. It's free; the Pro version costs $20 with a free 30-day trial period.