This is a really simple addon that answers the question, how long till I reach the next lvl.
What is does it figures out how much xp you are getting per second and uses this to give you a time to next lvl. It has been accurate for me on both a new  lvl 1 and my lvl 61.

Every time you gain XP it will simply add the amount of time left to the chat window. If the time is increasing it means you are slowing down and should kill faster or more to a new area.

I use it to figure out how much time I need to log before the weekend so I can join my guild in dungeons.

Extra Commands:
/xpt
/xp_timer
Either one does the same thing.. It give you more stats such as logged in time and total xp gained since login. IT will also tell you how many of the last xp you got you need to get the next lvl (kills) so you can know that you can just hunt 15 more of what ever you are hunting and you will get that lvl (then log out to go to bed or something).

/xp_timer_reset
Resets all values. If you are helping out in a low lvl for a few hours and then you move on to a higher XP area the timer will think that you took 4 hours to kill your first monster and there for will just call you slow. Resetting the timer will allow it to make better calculations.

With version 3.1
Added Cash timer feature and general updates.
Commands:
 /ct
 /cash_timer
Find out how much money you've been making, great for finding out how much more grinding you need to to to buy that new mount of item.

/ct_reset
to reset the information and give you a fresh count (should not be needed)

information is saved even if you log out.

Commands to control how often you see the time update
/xp_timer_on
/xp_timer_off

The standard commands such as /xpt still work when it is off.

I am always looking for suggestions and feature requests so don’t be shy to contact me at addon (at) phansoft.ca