Dragon bones are sort of cheap now, 99 Prayer would be cool!
99 Hunter will also be fun too, you could make a heck of money through grenwall spikes.
96 Herblore would be quite useful for overloads, wouldn't cost too much now that a lot of potions & herbs have crashed.
88/96 Summoning by killing wyverns/waterfiends/rock lobsters for charms can be done, wyverns are profitable I believe and 88/96 Summoning is very useful to have!
If not any of the above, Slayer is fun, train it up high, make money with it & then when Jagex releases a Slayer update you'll be good for gold

~Abs