I am not a fan of using SQL*PLUS as an interface to Oracle. I usually use yasql, but it hasn\'t been updated since 2005 and can do with some improvements. A quick Google searc
TOAD is pretty expensive, but you can download a 90-day trial from the Quest site to see if it's got the feature set you want (don't be fooled by the "freeware" title - it's only free for 90 days, and then it expires, which definitely makes it shareware):
http://www.toadworld.com/Freeware/ToadforOracleFreeware/tabid/558/Default.aspx
Another options is a tool I've seen on CodeProject:
http://www.codeproject.com/KB/database/OQuery.aspx
It's in .NET, so you'd have to see if it compiled on Mono, but it might be worth a shot. I haven't used either tool (Toad or this one), since I'm a SQL Server guy, but I've heard good things about Toad.