Diablo. That damn game has a lot to answer for.
On 56k modem. My housemates at Uni couldn't get on the phone line between 10pm to around 5/6am as I was on Diablo. £200 a month telephone bill as average for me back then.
I was into a lot of LAN stuff back then as well - namely Quake2/3, Starcraft and the occasional bit of HalfLife Deathmatch, as well as some UT.
Quake 3 consumed me when Diablo started drying up as I'd 'upgraded' to 64Kb/128Kb BT ISDN 'Home highway' lines.
Phone Bill doubled *winces*
Left Uni, got wise and just played offline stuff until Broadband/flat fee come around. But fun online times back then.