have a look at the premier equine site, they do lots of boots that would be suitable
for jumping I would want something to guard the tendon, but for low levels some people use brushing boots
Cross country you are more likely to take a few knocks so i would suggest something that gives more allround protection like wraps, that way you are supporting the tendon and the front of the leg as the jumps are fixed.
For show jumping i would suggest open fronted tendon boots on both front and rear. That way you are supporting the tendon but allowing the horse to feel the pole if it knocks one and is more likely to pick their feet up higher next time. You can also get some nice open fronted tendon boots for the rear as well that look very smart, they look like a shorter version of the normal front tendon boots or you can get ones that are even long that the front tendons that come all the way up their legs to their hocks (i like these and they look good - but is personal preference).
I always jump in full tendon wraps. If you work your horse in tendon boots all the time it actually weakens their tendons as they get used to relying on them. Some wraps have inbuilt strike pads if your horse brushes, mine doesn't so I opted without. I agree with jo open tendons are an option for show jumping, but I only use regular fetlock boots on the back, less likely to be injured (in my opinion).
I bought my wraps on ebay, they were brand new and started at about £12 or buy it now £18ish. They are just as good as the big name ones but I don't cry everytime I jump through the dirty water jump!!!!!
on ebay just search 'training wrap' and if they're still on there you'll find them, the sizing is pretty accurate.
premier equine ones are very good and not silly money either.
otherwise, i really rate NEW boots.
i'd recommend something with tendon guards for xc, nothing to overheat the leg, good pair of shortish overreach boots for any jumping, and open-fronted sj boots.
for SJ i love my Veredus Carbo Gel boots, if your budget isnt that big then they do the same without the gel (much cheaper) i have used veredus boots for years and love them.
for xc i only do low level (when i go - about 3 times a year) i have a set of eskadron xc boots, really like them easy to put on my over excited tb when at the xc and wash up great