Python, 978 980 981 980
import sys,random
f=open(sys.argv[1]).read().split('\n')
s=t=[]
d=p=x=y=k=0
r='n'
h='0123456789abcdef'
while h:
c=f[y][x]
if k:k=0
elif p:
if c==p:p=0
else:s+=[ord(c)]
else:
for l in (h+'''0123456789abcdef`s+=[h.find(c)]
><^v`d='><^v'.find(c)
x`d=random.randint(0,3)
/`d=(d+2)%4
\`d=3-d
|#`if d<2:d=1-d
_#`if d>1:d=5-d
+-*,%=)($gp`a,b=s[-2:];s=s[:-2]
+-*%`s+=[eval('a%sb'%c)]
,`s+=[a/b]
=`s+=[a==b]
(`s+=[a<b]
)`s+=[a>b]
'"`p=c
!?`if(s[-1]==0)or(not s)or('or'!'==c) or s[-1]==0:k=1
:`s+=s[-1:]
~`s.pop()
$`s+=[b,a]
@`s=s[:-3]+s[-1:]+s[-3:-1]
&`s,r=(s[:-1],s[-1])if r=='n'else (s+[r],'n')
.`s,t=t,s
r`s.reverse()
}`s=[:-1]+s[-1:]
{`s=s[1:]+s[:1]
m`s,t=[],s+t
g`s+=[f[b][a]]
p`f[s.pop()][b]=a
on`z=chr if c=='o'else str;sys.stdout.write(z(s.pop()));sys.stdout.flush()
i`s+=[int(sys.stdin.read(1))]
;`h=0''').split('\n'):
l=l.split('`')
if c in l[0]:
try:exec(l[1])
except:0
if d<2:x=(x-d*2+1)%len(f[y])
else:
while 1:
try:y=(y+d*2-5)%len(f);f[y][x];break
except:0
This is a work in progress. It doesn'tDoesn't support threading ([ and ]) yet, and it could be optimized a lot. I'll come to that later. By now, it's just the shortest interpreter here.
Versions:
1. 981
2. 980: Fixed p instruction; small improvement.
3. 978: Fixed ? instruction.