Grapple check is based on BAB. So if you wants to be the greatest grappler, monk is not the best choice. Take some full-BAB class(es), maybe Barbarian, then proceed to Reaping Mauler prestige class.
Reaping Mauler is pretty awful, IMO.
Full BAB and Imp. Grapple are the basics. Being as large as possible really helps. The PGtF has a regional feat (Jotenbrund?) that lets you count as a size larger for many things. Goliath (RoS) and Half-Giant (XPH) races get powerful build, also counting as a size larger (both +1 LA). Or just play a Half-Ogre (RoD, +2 LA) and be large, reach included. Alternatively, be a druid. You get medium BAB, but a form w/ huge str and largest size possible (look to bears and dinosaurs, generally) more than make up for it. Also, with Spell Compendium, unless your DM (justifiably) rules no, you can stack wildshape with "bite of the x" spells. I recall the level 5 version is bite of the weretiger and gives something like +16 str.
Getting Enlarge Person potions or tattoos of Expansion (depending on if you're humanoid or not) give you +5 on grapple checks each time, well worth it.
The feats named already are pretty good, can't really think of many feats for grappling. It's mostly the class, race, and items you choose. MIC has some good items to add to your grapple modifier.
With Tome of Battle, you could either play as a Warblade and learn Tiger Claw and Stone Dragon maneuvers or take them as feats, but those disciplines have some nice things for grapplers. Namely, stances. TC has wolverine's stance, which lets you use any one-handed or light weapon in a grapple and w/o the -4 penalty. SD has a stance called crushing weight of the mountain, which gives you a constrict attack for 2d6 +1.5x str mod. Taken as feats, both would require knowing a maneuver from the discipline first and 10+ HD.