The Trick here is to predict who's interested
The race for the KOM prize is one weird competition. If the Tour were high school, the KOM winner would get the "Coolest Guy" award. But it's not obvious before the race who will wind up seriously challenging for the prize. Even riders who have said they will want the jersey may not, as the race unfolds poorly for them (possibly by doing to well) actually challenge for it.
So you can't make a list of riders who are definitely competing for the prize ahead of time. Well, actually you can but that list is almost guaranteed to be wrong because who actually winds up competing for the spotty jersey mostly depends on how the race for the General Classification unfolds. What happens is that you get a few aggressive riders in the early stages where the climbs are low and people wonder if any of them are gonna try to stick it out in the Alps and Pyrenees. Almost always they don't. Then you get the first Cat 2, and Cat 1 climbs and riders start to make themselves known. By this point though the KOM prize is still getting mixed up with the overall prize in that the big race favorites aren't gonna let anyone just escape to claim the climbing points as that rider might then take a decisive race lead. Instead, look for riders who are already several minutes back and thus are no threat to the overall lead to make their moves. Usually we are talking about two-three riders at this point fighting it out over the last half of the race. It should be mentioned that there's the slight possibility that the leader of the General Classification might take the prize. It's rare but usually the GC winner is #2 or #3 in the KOM race as well so there's always that possibility if there is not otherwise a clear KOM leader.
Sound complicated? Actually it isn't. This year, as in most years, expect the winner to snag around 160-200 points with the second place rider well behind at less than 140.
How the points are won
There are five categories of climbs. Here they are with the points that the first riders to crest them earn:
Cat 4: 3, 2, and 1 point for the first three riders.
Cat 3: 4,3,2, and 1 point for the first four riders.
Cat 2: 10, 9, 8, 7, 6, and 5 points for the first six riders.
Cat 1: 15, 13, 11, 9, 8, 7, 6, and 5 points for the first eight riders.
Hors Categorie (HC): 20, 18, 16, 14, 12, 10, 8, 7, 6, and 5 points for the first 10 riders to crest the hill.
Important Note: If a Cat 2, 1, or HC climbs is the last climb of the stage its points are doubled. Those stages are with the category of climb involved are: stage 7-Cat 2, 8-Cat 1, 9-Cat HC, 10-Cat 2, 12-Cat 2, 14-Cat 1, 15-Cat HC, 16-Cat HC, and stage 17-Cat HC
Kind obvious that those riders who can get over the high finishing climbs first will get the lion's share of the KOM points, no?
So who might we expect to be contesting for the prize? Before I go into some names, realize again that this competition doesn't reveal itself until we are actually in the mountains. There are no current riders that target this competition year after year like Richard Virenque did in the 90's. But there are a couple of likely suspects:
1. Egoi Martinez, Euskaltel
Why? He's making a career of snagging KOM jerseys in various stage races. He was second in the competition in last year's Tour, and won the KOM in the 2006 Vuelta. Lately he's won the KOM jerseys at this year's Dauphine, and last year's Pais Vasco, and Tirreno-Adriatico. Look to see if he drops back in the overall race before we hit the Jura and Alps. If so bank on him making a strong play.
2. Pierrick Fedrigo, Bbox
Why? Good climber who won't sniff the head of the race, he will definitely be stage hunting in the mountains. If that stage hunting proves successful early on we may see him contest the KOM prize. Or not.
3. David Moncoutie, Cofidis Why? Two-time winner of the KOM prize in the Vuelta (in 08 and 09) I can imagine him topping of his palmares before retiring with a spotty jersey, can't you? In fact I'll make him the sentimental favorite. He has won two Tour stages in his career.
edit- Maybe Damiano Cunego as suggested by agi? eh?
4. Matthew Lloyd, Omega Pharma Lotto
Why? He won the KOM prize at the Giro in May and how cool would it be to win both?
5. Joaquin Rodriguez, Katusha
Why? Cause he's the best climber in the bunch. If he falls of the pace of the GC competition look for him hunting the spots. Hell, even if he doesn't fall off the pace.
Other riders could be mentioned-and will in the comments. The KOM race won't start to take shape until week two. We'll come back then to see where we stand.