You mean issues he's been beaten, or ones he kicks ass in? If ones he kicks ass in then check out the Fatal Attraction issues, I think I have them all, (looking for the issue I wanted to bring up

).
K, the ones I could find are Uncanny X-Men 304, Wolverine 75, X-Force 25, Excalibur 71, X-Factor 92. I can't remember if theirs another, I thought there was, but don't feel like looking thru all my comics for it.
Anyway in the Uncanny X-Men Magneto is kinda super charged and during Illyana's funeral he owns the X-Men more or less. There are members from the main X-Men, X-Factor, and X-Force teams, and he blocks Jeans psychic powers by "using his electro-magnetic powers to jam my (jean's) psionic powers", holds every last one (about 25+ x team members) on the ground and unable to move by magnetically gripping the Iron fibers in their blood, all while forcing Wolverine's claws to retract and ripping apart Xavier's chair and 'pulping' Senyaka with his own coil. This whole time he shows no sign of difficulty, and while doing all of this he's holding Avalon in orbit which is said -
"The Havoc Caused by the Leviathan that is Avalon's sudden presence -- It's violation of Earth's electro-Magnetic field -- will mar the landscape.. Will ravage the citizenry of the planet..for weeks to come".
The only reason they even get up is because Bishop absorbs the energy Magneto is giving out, Rogue tries to kiss him and he barely feels it which shocks her.
In the X-Force one he rips away Cables techno-organic side and about kills him, and Cable has stood up to the Hulk during the Onslaught saga. That entire series was a badass series of moments for Magneto once he came back (his acolytes were doing the damage until then). That scene where's he's holding down all those X-Men, including several very high super strength individuals, while holding up avalon, and attacking just put him in another level to me.