Emacs is the best. It's written in an old dialect of Lisp itself, and you can customize it and script sequences of actions in it with Lisp. It also has SLIME, which is the Superior Lisp Interaction Mode for Emacs, (see http://common-lisp.net/project/slime/), which is the most amazing IDE I have ever seen for any language, and I've used VS.NET and Eclipse and all the rest.
That's for Common Lisp (CL), which you may or may not want to develop in; I personally frequently choose to write in CL because it has a very large library, and because it has SLIME.
For Scheme, Emacs is also good, but there isn't something analogous to SLIME.
SLIME has go-to-definition of a function as one of its more basic features, along with auto-completion, convenient listings of arguments when you first write down a call to a particular function, and much more.
I have a quick question that I can't justify creating a new thread about. Since you brought up Lisp implementations though...
I was about to choose to write my programs with SBCL, but it looks like the Win32 port isn't yet complete. Since I'm aiming towards using Lisp in games, speed is an issue, and so is running on Windows. Would you or anyone reccomend a dialect of Lisp which is fast and runs under Windows? Even just 1/4th the speed of C would be excellent.
Ask on the #lisp IRC channel on freenode about whether the SBCL win32 port is complete enough for your purposes. It's coming along. Remember to ask your question and then leave the chat idling, so that if your question isn't answered right away, people who have left it idling and then come back to it can see your question and then answer it.
I believe CLISP runs on Windows. I have no idea whether this is at all practical, since I don't use Windows, but maybe you could use a Unix emulator like Cygwin and run SBCL (and your game) in that, invisibly to the user?
Naturally, as a reader of YC news, I have also looked into LISP again lately. While I haven't really tried it yet, I found a LISP plugin for eclipse that is running SBCL on Windows. They claim to be inspired by SLIME. Not sure if it would be possible to get their SBCL to run on Windows standaline, but i was planning to use that plugin (sorry no link, but should be easy to Google).
That's for Common Lisp (CL), which you may or may not want to develop in; I personally frequently choose to write in CL because it has a very large library, and because it has SLIME.
For Scheme, Emacs is also good, but there isn't something analogous to SLIME.
SLIME has go-to-definition of a function as one of its more basic features, along with auto-completion, convenient listings of arguments when you first write down a call to a particular function, and much more.