Pipe clamps are a must. Seems like there is always a time when I can use them...
Never underestimate the power of a good set of chisels. Well sharpened chisels can square things very nicely as long as you are patient.
A 20 or 10 gallon fish tank. Seriously. My dad and I used to keep hardwood scraps in one and it makes for super easy browsing for just the right size.
Coffee Cans! Yes folks thats right! Standard coffee cans now come with a plastic sleeve because its cheaper than printing metal. It comes off easily and you are left with a fine modular container which fits perfectly on a shallow shelf. Need a lot in a hurry? Go to your local recycling plant. You can take 30 out of the bins and no one will bat an eye..
Make a cut light. Its a light outside your shop door that indicates you are cutting or working with heavy tools. Like a Dark Room light. Keeps people from barging in and you loosing a hand, finger, eye...etc...
Build a custom workbench thats tuned to your height. Mine is about 9 inches higher than a standard workbench. Keeps backaches away and makes it easier to build. The more fun you have in your shop, the more likely you are to be satisfied with your investment.
Carpet or Foam for the floors. Can stress this enough. Its a bitch to clean, but padding for your immediate work area can really take the strain off your ankles and knees for long stand up seassions. It also keeps the cold from seeping through to your joints in cold weather.
An extendable shop vac ( and this is important!) with an on off switch located at the head. Its SOOO much easier to keep a clean shop if you just grab the hose and whoosh it away. You would be surprised how often I dont vacuum when I have to go over, turn it on, walk back over, vacuum, then go over, turn it off, then go back to work...
Also...get to know your neighbor's kids. Cleaning a shop is easy to do for young folks and they seem to really like to do it, especially for cash! Plus, you become the "cool neighbor" who, by default, enjoys the privelege of not getting his house egged on cabbagestalk night and offers from young men to mow lawns, clean gutters and generally do all your stuff for you for 1/4 the price...
GOOD to be the cool neighbor...
and last but not least...
Music! Get an old receiver and a pair of old speakers and outfit with tunes. Tunes will help in all kinds of ways. Loud music for cleaning, gametime away from the wife, classical for small delicate cuts, jazz for creativity, country for when you have screwed it up...

and the best peice of advice Left...
Dont skimp on your table saw! Dont DIY it. Get a precision table with some rollers and plenty of space to move. Some can even be swapped for a router. Trust me on this one. Its worth the extra few bucks the first time you want to make a good cut on a piece more than 36 inches long.
Consider a chop/miter saw too. They can be awfully handy sometimes.
I could write a book...