I (think) I can claim 22 grounds, that I've watched RL at.

[uWatching Saints[/u
St Helens - Knowsley Road
Wigan - JJB & Central Park (+ 1 1995 WC game)
Warrington - Halliwell Jones (+ CC Semi Final)
Widnes - Stobart Stadium
Huddersfield - Galpharm (+ CC Semi Final(s)
Leigh - Hilton Park
Harlequins RL - The Stoop

[uWatching other Teams[/u
Dewsbury - The Tetley's Stadium
Sheffield - Don Valley
Gateshead - Gateshead International Stadium (Although I was only there to play American Football!)
Saints IMBRL vs Wigan IMBRL (now Wigan Riversiders) - City Road (Pilk Recs Old Ground).
Highfield - Hoghton Road (Sutton, St Helens) (The first game(s) of RL I ever watched!!!!!

[uWatching Finals[/u
Murrayfield - Challenge Cup Final
Millenium Stadium - Challenge Cup Finals
Old Wembley - 1 International
New Wembley - Challenge Cup Finals
Spotland Stadium Rochdale - National Cup Final - Thatto Heath vs Featherstone Lions.
Twickenham - Challenge Cup Final
Old Trafford - Grand Finals.
Reebok Stadium - World Club Challenge(s)

[uPlayed[/u
Bold Miners Ground

barrow ( craven park)
batley (mount pleasant)
bradford(odsal+valley parade)
bramley ( mclaren field)
carlisle ( gilford park)
catalans ( stade aime giral)
castleford ( jungle)
chorley ( victory park)
dewsbury( ram/tetleys stadium)
doncaster (tattersfield + belle vue)
featherstone ( post office road)
halifax ( thrum hall + shay)
harlequins/london (crystal palace+copthall stadium+griffin park+stoop)
highfield( hoghton road)
huddersfield( fartown+leeds road+galpharm)
hull( boulevard+ kc stadium)
hull kr (new craven park)
hunslet( elland road+ south leeds stadium)
keighley(cougar park)
leeds (headingley)
leigh( hilton park)
nottingham city( harvey haddon stadium)
oldham(watersheddings+hurst cross)
prescot panthers ( hope street)
rochdale (spotland)
st helens( knowsley road)
salford( willows)
swinton (gigg lane)
trafford borough (moss lane)
wakefield (belle vue)
warrington (wilderspool+ HJ stadium)
whitehaven (recreation ground)
widnes (naughton park/halton stadium)
wigan(central park + JJB)
workington (derwent park)
york(ryedale stadium)

I counted 56 in the UK Ive been to, 18 in NZ, 6 in France +
Jacksonville
Glen Mills Bulls
Univeristy of Philadelphia
Luzniki Stadium / Udina / Kazan Central / Lokomotiv Stadium in Russia

[uLeague and Cup matches involving Keighley[/u

Keighley - Cougar Park
Batley - Mount Pleasant
Barrow - Craven Park
Bradford - Odsal
Bramley - (1) Barley Mow, (2) McLaren Field
Blackpool - (1) Borough Park, (2) Blackpool Mechanics FC
Chorley Borough - Victory Park
Castleford - Wheldon Road
Cardiff Blue Dragons - Ninian Park
Carlisle -(1) Brunton Park, (2) Gilford Park
Dewsbury -(1) Crown Flatt, (2) Rams Stadium
Doncaster - Tattersfield
Featherstone - Post Office Road
Fulham - Craven Cottage
Gateshead - International Stadium
Halifax - Thrum Hall
Huddersfield -(1) Fartown, (2) The cold and windy monstrosity
Hull - The Boulevard
Hull KR -(1) Craven park, (2) New Craven Park
Hunslet- (1) Parkside, (2) Elland Road Greyhound Stadium, (3) Elland Road, (4) Mount Pleasant, (5) South Leeds Stadium
Huyton - Alt Park
Leigh - Hilton park
Leeds - Headingley
London Skolars - New River Stadium
Oldham - Watersheddings
Prescot Panthers - Spotland
Rochdale - (1) Athletics Gounds, (2) Spotland
=blueRuncorn Highfield - Canal Street One I had missed
Salford - The Weaste
St Helens - Knowsley road
Swinton - (1) Station Road, (2) Gigg Lane, (3) Sedgeley Park
Wakefield - Belle Vue
Warrington - Wilderspool
Widnes - Naughton park
Wigan - Central Park
Whitehaven - Recreation ground
Workington - Borough Park
York - (1) Clarence Street, (2) Ryedale Stadium

[uTest matches (TM), Internationals (I), Finals(I), World Club Challange(WCC) Tour games(TG)[/u

Old Trafford - TM, F, WCC,
Anfield - WCC
Post Office Road - TG
Elland Road - TM, I
Headingley - TM, I, F, TG
Millenium Stadium - F
Murrayfield - F
Twickenham - TM, F
Wembley - F, TM
Thrum Hall - WCC
=blueJJB - TM another one missed

plus lots of amateur games at various venues.

[uSuper League[/u

Bradford Bulls - Grattan Stadium
Castleford Tigers - The Jungle
Huddersfield Giants - Galpharm Stadium
Hull FC - KC Stadium
Hull Kingston Rovers - Craven Park
Leeds Rhinos - Headingly Carnegie Stadium
Salford City Reds - The Willows
St Helens RLFC - Knowsley Road
Wakefield Trinity Wildcats - Belle Vue
Warrington Wolves - Halliwell Jones Stadium
Wigan Warriors - JJB Stadium

[uChampionship[/u

Batley Bulldogs - Mount Pleasant
Halifax RLFC - The Shay
Leigh Centurions - Hilton Park

[uChampionship 1[/u

Dewsbury Rams - Tetley's Stadium
Oldham Roughyeds - Boundary Park
Rochdale Hornets - Spotland Stadium
Swinton Lions - Park Lane

[uNRL[/u

Brisbane Broncos - Suncorp Stadium (State of Origin)
Cronulla Sharks - Toyota Stadium
Gold Coast Titans - Skilled Park
Parramatta Eels - Parramatta Stadium
Sydney Roosters - Sydney Football Stadium
Wests Tigers - ANZ Stadium

[uOther[/u

Murrayfield - Murrayfield Magic
Reebok Stadium - World Club Challenge

most of the stadiums in the uk.never been to aus or nz.been to aime giral and stade brutas for catalan.
and did anyone else go to donnybrook in dublin jan 2006 for skolars v saints?i was there.