I have one ISP who provides me with multiple links, to allow me to loadshare I use BGP with metrics, this allows BGP to pick the best routes out and our architects to decide inbound balencing across our IP range. here is an example config. hope it helps.
router bgp XXXXX
no synchronization
network x.x.x.x mask 255.255.240.0
redistribute connected route-map to_BT
redistribute static route-map BGP_OUT
neighbor x.x.x.x remote-as 2856
neighbor x.x.x.x route-map BGP_MET_250 out
neighbor x.x.x.x remote-as 2856
neighbor x.x.x.x route-map BGP_MET_251 out
neighbor x.x.x.x remote-as 2856
neighbor x.x.x.x route-map BGP_MET_252 out
maximum-paths 3
route-map BGP_MET_252 permit 10
match ip address 50
set metric 10
!
route-map BGP_MET_252 permit 11
match ip address 60
set metric 10
!
route-map BGP_MET_252 permit 12
match ip address 70
set metric 10
!
route-map BGP_MET_252 permit 13
match ip address 80
set metric 10
!
route-map BGP_MET_252 permit 14
match ip address 81
!
route-map BGP_MET_250 permit 10
match ip address 40
set metric 10
!
route-map BGP_MET_250 permit 11
match ip address 60
set metric 10
!
route-map BGP_MET_250 permit 12
match ip address 70
set metric 10
!
route-map BGP_MET_250 permit 13
match ip address 80
set metric 10
!
route-map BGP_MET_250 permit 14
match ip address 81
!
route-map BGP_MET_251 permit 10
match ip address 40
set metric 10
!
route-map BGP_MET_251 permit 11
match ip address 50
set metric 10
!
route-map BGP_MET_251 permit 13
match ip address 51
access-list 10 permit x.x.x.x 0.0.15.255
access-list 20 permit x.x.x.x 0.0.2.255
access-list 20 permit x.x.x.x 0.0.15.255
access-list 40 permit x.x.x.x 0.0.7.255
access-list 41 permit any
access-list 50 permit x.x.x.x 0.0.0.255
access-list 51 permit any
access-list 60 permit x.x.x.x 0.0.0.255
access-list 70 permit x.x.x.x 0.0.0.255
access-list 80 permit x.x.x.x 0.0.3.255
access-list 81 permit any