The Ducati Monster List web site (http://www.ducatimonster.org/) is full of interesting chatter about riding and modifying monsters. It has one unpleasant side effect though - if you spend even a few minutes on the site you tend to get excited about making changes to the bike. Things that you previously didn't even notice, now really really bug you. The #emissions_cannister for example

Spare parts catalog - http://www.ducati.com/bikes/catalogs.jhtml;MY=2002

Hacks

suspension

http://www.computrackboston.com/ - local place that does suspension setup/upgrades

reflectors

Everyone removes the reflectors from the front forks. I hadn't noticed until I read about it, and then sure enough they started to bug me. They're nasty little plastic things stuck on with double-sided tape. They're clearly tacked on at the last minute to meet some regulation or other. The good news is that they're easy to remove with a hair dryer and a little elbow grease. One almost fell off, the other needed a little convincing with a screwdriver. Afterwards the forks needed a little cleanup with some alcohol to get rid of the crusty glue that the adhesive tape had left behind.

gas tank stickers

Again, a little heat with a hair dryer and some careful peeling got the two gas tank stickers up. A better idea than the hair dryer is to just leave the bike in the sun for an hour or two - I'd bet this will heat the tank more than the hair dryer.

I stuck the stickers on the inside cover of my owner's manual just so I have them for reference.

emissions cannister

Purely cosmetic, but it's surprising how much better it looks when it's done.

http://www.ducatimonster.org/faq/faq_emissions.html

http://pg.photos.yahoo.com/ph/jerseyjeffshinn/album?.dir=c233&.src=ph&store=&prodid=&.done=http%3a//pg.photos.yahoo.com/ph/jerseyjeffshinn/my_photos

exhaust

You can hack on the stock exhausts to make them louder: http://home.earthlink.net/~desmoduck/muffler_mod.html

Or you can pay someone to do it: http://www.ducatipipemod.com/. I went this route (got the "1/2 mod") and it's amazing how much of a difference it makes. It's a little louder (but not obnoxiously loud) but the sound is magnificent. Not as deep as a Termignioni or Arrow but great value for the money.

rear brake

http://www.tcmproducts.com/Ducati_Rotors.html will drill lots of holes in your rear brake rotor to make it lighter.

Mirrors

http://www.dual-star.com/index2/Equipment/adjustable_mirror1.htm - inexpensive, mounts on the handlebar. Pix on a monster at http://www.ducatimonster.org/smf/index.php/topic,8750.0.html .

http://www.constructorsrg.com/products.html - expensive but very high quality.

Turn Signals

http://www.custombike.org/shock_racing_marker_lights.htm - LED's, about $25

http://www.cyclegear.com/spgm.cfm?L1=3&L2=&L3=&L4=&item=MRX_OI1_G - look like OEM, but smaller. Bulbs.

Horn

You can never be too loud.

http://www.ridesafer.com/page/mfc0/Home.html

License Plate Lights

http://www.watsendesign.com/products/current/LEDPLATELIGHT/index.html
http://www.4strokesonly.com/LicensePlateLights.html

Cool Paint

http://www.frostysfinishes.com/ - guy in NH that does some amazing stuff with paint.

Track Days

I'd like to ride the duc on a track sometime.

http://www.tonystrackdays.com/ - program for beginners, sounds good.
http://www.nesba.com/ - a group that runs track days.
http://www.teamdaemon.com/ - two track days a year at Loudon.
http://www.penguinracing.com/ - more focussed on instruction.