Be sure to look at the Suzuki DRZ 400 (especially if you are over 6 feet tall). Its a four stroke, comes with electric start, very reasonably priced and a great trail bike.
Huska's are nice bikes, but hard to find and even harder to get parts for (plus very expensive).
KTMs are good bikes. The 300 and 400 are a little shallow on power though. I guess it depends on how much power you want though. They have a lot more power than you friends TT 225. If you want pure power the 520 is the perfect. Its heavy with sluggish suspension, but with 50 hp its hard to get the smile off your face after you ride it. Downside though, the KTMs are the most expensive of the major manufacturers.
Honda doesnt make a good trail bike in my opinion. The XRs are just too heavy. They are great for open desert rides, but just pigs on tight trails.
Yamaha is the best ( I only say that because I ride a YZ400f)
The WRs are good trail bikes and pretty good price wise. If you dont want tons of power it would be hard to beat the WR250. Its light, great power for a 250 fourstroke, and nimble with great off-the-shelf suspension. The WR 426 has a lot more power, but is quite a bit more heavy.
Kawasaki.. hmm.. I can't even think of a Kawa trail bike.
Suzuki has the new DRZ 400s. But have been plagued with a bad reputation for dependability because of their 2strokers. Most riders will scuff at a Suzuki, but of the 2 Suzukis my friends own.. the DRZ400 hasnt had a single problem in 2 years.. and a RM 125 that lasted for 8 years with normal maint. and 2 top end rebuilds. The RM 125 was retired for a YZ250F though. Suzuki's are the least expensive of the group as well.
No matter which way you go.. they are all good bikes. 4strokes are the way to go for trails. The 2strokes are a dying breed (still the best for racing though) and too fussy to be worth it with all the new 4 strokers on the market now.
So good luck.. and post what you get.. and invest in good health insurance:D