Jetstar are a major player at Singapore with their A320s:

9V-JSI Jetstar Asia Airways A320 at Singapore Changi WSSS by AeroPics, on Flickr

9V-JSP Jetstar Asia A320 at Singapore Changi WSSS by AeroPics, on Flickr

9V-JSB Jetastar Asia (Valuair) A320 at Singapore Changi WSSS by AeroPics, on Flickr
... and A330s:

VH-EBR Jetstar Airways A332 at Singapore Changi WSSS by AeroPics, on Flickr
LOts of other low cost airlines have a prescence at Singapore, including the infamous Lion Air:

PK-LKF Lion Air B739 at Singapore Changi WSSS by AeroPics, on Flickr
Indonesia Air Asia:

PK-AXI Indonesia Ai Asia A320 at Singapore Changi WSSS by AeroPics, on Flickr
Even though the Kangaroo Route flights now go through Dubai, Qantas maintains a considerable presence with 5 flights a day operated by A330s and 747s:

VH-QPC Qantas A333 at Singapore WSSS by AeroPics, on Flickr

VH-OEH Qantas B744 at Singapore Changi WSSS by AeroPics, on Flickr
Cathay Pacific also maintains a very large presence with no less than 10 flights a day:

B-HNA Cathay Pacific B772 at Singapore Changi WSSS by AeroPics, on Flickr
Singapore Airlines is however dominant:

9V-SRK Singapore AIrlines B772 at Singapore Changi WSSS by AeroPics, on Flickr

9V-SYF Singapore Airlines B773 at Singapore Changi WSSS by AeroPics, on Flickr

9V-STN Singapore Airlines A333 at Singapore Changi WSSS by AeroPics, on Flickr

9V-SKE Singapore Airlines A388 at Singapore Changi WSSS by AeroPics, on Flickr
Singapore Airlines maintains a greater presence still through its subsidiaries: Silkair

9V-SLF Silk Air A320 at Singapore Changi WSSS by AeroPics, on Flickr
And its new long haul low cost subsiduary - Scoot, whose 777s have grown on me! Quite quirky branding!

9V-OTB Scoot B772 at Singapore Changi WSSS by AeroPics, on Flickr
Quite a few freighters also visit Singapore:

OO-THA TNT Airways B744 at Singapore Changi WSSS by AeroPics, on Flickr

LX-VCG Cargolux B748 at Singapore Changi WSSS by AeroPics, on Flickr
Whilst Garuda sends their A330:

PK-GPM Garuda Indonesia A332 at SIngapore Changi WSSS by AeroPics, on Flickr
And JAL their 787 - my first catch of a Dreamliner:

JA825J Japan Airlines B788 at SIngapore Changi WSSS by AeroPics, on Flickr