Cleric anything is viable, as is Wizard anything.
Rogue 1 / Lore Bard 19 is as good an old fashioned Skill Monkey as any , and
you get to be a top caster.http://www.giantitp.com/forums/showthread.php?490505-The-Social-God-A-guide-to-an-optimized-party-face
Paladin 6 / Sorc 14 is a burst damage combo (and similars) that got the most attention, still ongoing.http://www.giantitp.com/forums/showthread.php?502673-Unlimited-Blade-Works-The-Guide-to-the-Ultimate-Paladin-Sorcerer-Multiclass
Barb 3 Bear and 6 Eagle / Druid 11 , and stuff as many goodies onto the 1 mile
sight range. Call it Radar. It tickles 3.0e Divine Rank 1 memories. iirc Sambojin did the best one around here.
Fighter 11 / Rogue 9 is an all the way down to Basic/SRD damage leader, and go up from there, to more specialties and better stuff like what SorO posted.
Gishes don't totally scan from 3.5. The various 2 attack casters ... are casters (that happen to be not completely incompetent, if stuck in combat). Valor Bard was an early fave but hasn't aged well, TreantMonk recently took this view of valor, i.e. Lore is better. Bladesinger Wiz got 3 different guides over at giantitp. Blade'Lock were nearly unusable until Hexblade in Xanathars. UA Old Favored Soul Sorc works and is tasty, but was replaced by UA New Favored Soul and then replaced again by Divine Soul in Xan.
For lack of a better term, the various Spell Banks, are cheesy and break the gentleman's agreement, and a few more reasonable No's. Necromancer army of the dead, is legal but a pain in the !@#$. Sorc+Lock+nosleep = most people can't do the argument anyway and is got a well earned tweet-rata. Glyph of Warding with a Bag of Holding to move it around is probably the best (shhh don't tell secret). Spamming Leomund's Hut is daily nova, but wotc put out some demons with Dispel Magic at-will = nope. Spamming Rope Trick is encounter nova, probably not too bad, wants teammates to spam with it, but see demon dispel.
Goblin + Revised Ranger in UA + Hunter, or Gloomstalker if you can swing it, is a straight to the point archer. Dex, dex, Sharpshooter for feats.
Sorc Divine Soul + Tome 'Lock without breakage, is a fun spreadsheet-of-options build stub. Spamming disguise self + disguise prof + expertise + Friends cantrip, is downright disruptive, technically totally r.a.i.