For example: I’d like to be a competent surfer—I’d be extremely happy if I could just stand up on a regular basis! (As it is, I’m just a lowly boogie-boarder)
And I’d really like to have the strength, skills, and stamina to compete in an world-class adventure race:the Eco-Challenge, for example.
I’ve always wanted to surf, since I was a little kid. Now I’m too old. I destroyed both of my knees in high school. I’d love to be able to run.
I would love to be able to enter a motorcycle in the Dakar Rally, but I’m not that good of a rider nor have the kind of money needed to field and entry, and I’ve always told people that the one sports skill I’ve always wanted to have is the ability to consistently kick 60-yard field goals.
Archery is what I’d like to master, and I am taking steps to do so. I bought my first set of practice arrows today with a quiver, glove, and bow stringer*. My brother took me to a local park with a range, and I’m happy to report I hit the target every time. I even managed a nice cluster of all six arrows on my last try.
As for other sports, I’ve tried many throughout my life: gymnastics, horseback riding, tennis, badminton, and competition target shooting. Gymnastics is the only one I wish I would have continued. I’m too old, now, though.
*I don’t have the upper body strength to string the bow myself…yet! 
I’m reasonably good (read: much better than the average bear) at the following:
It would have been nice to be a real contender at some point in my life.
I am training to do triathlons (sprint/olympic) this summer. Hoping to win/place/show in my age group (40 - 44). 
I will run a marathon one day…so far I can do 5 miles!
Umm…more exercise eh? Well getting a black belt would be cool!
before i get officially old, i think i wanna do the ironman triathalon. i’ve got some weird, ungodly stamina. i used to swim like crazy and i got the ton of fun know as the mile in competitions. yay me
Surfing and snowboarding.
Learned how to snowboard last winter (although I’m hardly competent); tried surfing last year in Australia…couldn’t stand up on the board. Maybe next time.
Hopefully going to try paintball soon.
I used to race in triathlons and I’ve done a marathon, and an Ironman seems very do-able for me. Only thing really holding me back is I don’t have enough time to train for those kinds of distances. Maybe someday…
Proficiency in the hard hitting, accuracate use of a sledgehammer or any hammer for that matter. I’d also to throw really well, especially rocks.
I would love to be able to ride really well. I do okay, but there’s so much better I could ride. I can’t afford to keep my horse and train, though. And even if I could still afford lessons, I doubt I could afford the lessons I need to make me really ride well. I’d like to be a competitive 3-day eventer.
As for a second sport…I’ve always found running to be fascinating. I don’t have the knees for it, alas. Too many years of riding, I guess.
StG
I used to be a competitive fencer, and I wouldn’t mind being able to get back there again. I just don’t have a spare 6-8 hours a day for training any more.
I wish I could be a competant gymnast.
I’d kill to be a competition level bull rider.
Cricket
Cricket
If I could do anything I wanted to in sports, I’d like to win the 100m dash at the next Olympics and be known as “The World’s Fastest Human”.
Oh, you mean something reasonable? Well then, I’d like to become fully competent in the operation of a sailboat.
Hammer throw. The coolest, wildest event in all of Olympic sports.
Hydroplane racing.
I want to finish a marathon. Since I haven’t actually started one yet, I have a ways to go. Still, my first 10k is the week after next, and I can already do 16k in practice, so I think I could give it a shot before the end of this year.
I’d really like to be good at shooting, but that ain’t gonna happen while I’m living here.
I’d like to be a kick-arse fencer. I did it for a couple of years at uni but it would be great to be world class at it.
Second sport…is skydiving a sport? I’d like to be really good at that. I want people to say: “Noone can fall out of a plane like him!”
I’d like to be able to run, at all. Like people in the movies, who are being chased or chasing someone and can run when called upon. My main impedence to this is me being horribly fat.
I’d like to be better at karate, and maaaaaybe someday competitive sparring. Lucky for me I can train while still fat and hopefully won’t be too old to fight before I am proficient (and thinner). Right now from what I can tell from my limited training that most of the skill in sparring is mental, and I can work on that for now.
Some realistic martial art. I trained ju-jutsu when I was young, and I just love the hell out of competing in something like that. It may be the primitive caveman warrior in me, but two guys standing off against each other just lights a flame in my heart. Also, it would make me feel that little bit safer in everyday living.
Long-distance running. Endurance is the coolest thing ever. I’m currently planning to run a tough thirty-kilometer cross-country race this autumn, and then a marathon in spring of 2007.
Cricket. But not a player; I’d like to be a competent umpire.
Second sport? I’ve fancied archery once or twice.