Plataformers
SMBros.
SMWorld
SMLand
SMLand 2
SM64
SMSunshine
SMGalaxy2
NSMB2

Umm... You mean played to the very end?

Mario Kart Wii.

I bore easily.

Super Mario World, 64, Sunshine, Galaxy 1/2, 3D Land.

I don't like the 2D ones that much.

Super Mario Galaxy 1 and 2
NSMB
NSMBW
SM3DL
NSMB2
MKDS
MKW
MK7
Mario Hoops 3 on 3
Super Mario 64 DS
Mario and Luigi;Bowser's Inside Story
Mario Tennis Open

13 Mario Games

One, something about a hotel. 

Hi, whats ur name.

I've played Mario games but never actually gotten around to beating any of them.

What is considered a Mario game? everything with the word Mario on it? or only the main series like 1, 2, 3, world, 64, etc?

Seriously, probably 100. I've been playing mario for YEARS.

Uh that's a good question! And for some games, "beaten" is hard to define... 
From the top of my head, counting only those with Mario in the title:

10 Sidescrollers:
SMB 1-3, Lost Levels (in SMAS), SML, SML2, SMW, SMW2 (Yoshi's Island), NSMB, NSMBWii

5 3D games:
SM64, Sunshine, Galaxy 1+2, SM3DL

5 RPG's:
SMRPG, Paper Mario, TTYD, Mario&Luigi 2-3 (not quite beaten M&L 1 and SPM)

6 Karts (not quite beaten MK64)
Double Dash

1 Sports:
Mario Tennis

= 27, my favourites in each category are bolded.