Hello and Welcome to the Ultima Server. Many of the changes have been mentioned already like the 3x base exp rate (2x after level 160), and the max exp ends at 96M, along with the often appearing Happy Hours (3x drops for 3 hours) and better spawn for rare monsters and Rare Monsters Events (increased rare monster spawns for up to about a week). Server Events happen quite often (Currently it is the Aniversary Event. This was preceded by the Triforce Event and Summer Event, and coming up next is the Christmas Event where Parasitic Gene Flow! will drop). While there isn't a complete comprehensive list of item changes yet, a topic aiming to do so was recently created. I main fonewearl on this server and the various buffs make it far more bearable than vanilla. If you guys need any help leveling, I am usually on my foney -Saith, just hit me up an we can very easily level with the 5x exp days of this event.
Here are a number of links you might find useful:
5th Aniversary Event currently on
http://www.phantasystaronline.net/forum/index.php?/topic/10414-5th-anniversary-ultima-event/
Max Stats Increase Patch, most stats max up by +100
http://www.phantasystaronline.net/forum/index.php?/topic/2727-update-patch-25/
Commands in Game (/npc 6 and above require the default outfit on your character to work, if you don't and try to log in, you will crash and need to go dressing room to change your character back, usually just hair, to what it was in order to log in again. Changing hair color affects the npc chars hair colors too! Also the common bank is buggy I advise against using it for valuable items.)
http://www.phantasystaronline.net/forum/index.php?/topic/70-commands-in-game/
Item Effects (the previously mentioned list of items including server changes to them)
http://www.phantasystaronline.net/forum/index.php?/topic/10353-psobb-item-effect-ie/
Some nice buffs to Force weapons, notably pwand and mg+
http://www.phantasystaronline.net/forum/index.php?/topic/7435-foweps-increase-little-more/
Wedding Dress Buff and New Shambertin Drops (some of the shambertin drops are acquirable elsewhere)
http://www.phantasystaronline.net/forum/index.php?/topic/2376-wedding-dress-and-shambertin/
Unofficial Ventrilo Voice Server run by Team PRO, open to all (You have nothing to lose but your keyboard chains!)
http://www.phantasystaronline.net/forum/index.php?/topic/10123-ultima-ventrilo-voice-server/