Watford = The Hornets.

Cardiff - Bluebirds

Swansea - Swans or Jacks

Leicester - Foxes

Chesterfield - Spireites

QPR - The Hoops

Plymouth - The Pilgrims

Notts Forest- Forest or the Reds

Bristol City - Idiots only kiddin the robins

Derby - The Rams

Just a couple i know of from following cardiff round the country

Northampton The Cobblers

BHA:

(1) The Seagulls

(2) The Albion

In addition to the above, I have no direct knowledge as I've neer been able to see any of these teams play myself apart from finally catching a Swansea game now that they are in EPL.  However, Wikipedia (the final arbiter of truth in the world) has the following team nicknames listed:

Brentford- the Bees

Bristol - the Robins, the Reds, the Cider Army

Carlisle - The Cumbrians, the Blue Army, the Blues

Coventry - The Sky Blues

Crewe - The Railwaymen, The Alex

Dag & Red - the Daggers

Hereford - the Bulls, the Whites

Leeds - the Whites, the Peacocks

Lewes - the Rooks

Lincoln - the Imps or the Red Imps

Northampton Town - The Cobblers, Tayn, the Shoe Army *Bonus Note* the Cobblers changed their badge emblem last season back to a prior version, so ours is now outdated

Oldham - the Latics

Port Vale - the Valients, the Vale

PNE - the Lilywhites, North End

Sheffield - the Blades

Southend U - The Shrimpers (I never bothered to look close enough to see that the lower left image on the shield is a shrimp), the Seasiders

Swindon Town - the Robins, The Reds, The Town

Tranmere - Super Whites, Rovers

Watford - The Hornets as James notes, though I like the local color: "the 'Orns"

Weston-super-Mare - The Seagulls

Wycombe - the Chairboys, the Blues

So, what the heck is a Chairboy?

The spireites? C'mon.  Don't saddle me with that.  I have a hard enough time getting out of Division III as it is.  That sounds like the name of our cheerleading squad.

CAFC, aka CRE:

(1) Motley Crewe

(2) Red, White and Crewe

(3) Cheshire Cats

(4) Alexandra the Great

(5) Gresty Road Bullies

then whatever else Wikipedia thinks.

Just found another nickname for BHA: The Limpets

Thank you guys for all your help.   I appreciate it!!!  This info will start to show up in the previews in the future.

Somewhere (well probably in Chesterfield I guess) a Chairman is getting a request from a gentleman in rural Missouri to change their nickname!  :-)  

As a Life Long Southend United I beg to dissagree with the above comment

Southend U - The Shrimpers (I never bothered to look close enough to see that the lower left image on the shield is a shrimp), the Seasiders

Actually Southend Un ited are : THE BLUES

 as a visit to any Home Game will educate you ...'Come on You Blues' can be heard echoing around the half empty stands, agreed ocasionally you will here a chorus of...

Sea Sea Seasiders Sea Sea Seasiders. 

The club mascots are Sammy the Shrimp & Elvis EEL but I cant remember us being called The EELS ever!

So primarilly we are

THE BLUES

then SEASIDERS 

& if you must 

SHRIMPERS 

although the fleet of fishing Smacks just up the River Thamesmostly catch COCKLES, not many Shrimps in the Thames Estuary these days

Database updated for you Mr. Dowson.   Great information and background.