In terms of the common methods offering incentives such as sponsorship, discount codes and product incentives are common but you need to ensure disclaimer are made in the right way and any links pointing back to your site contain a rel='nofollow' tag in the link code.

For search engine purposes you need to make sure any links coming to the site are stated appropriately with nofollow tags. Google recently provided further guidance on this area shown at https://webmasters.googleblog.com/2016/03/best-practices-for-bloggers-reviewing.html

Also you may want to see if the blog has a suitable disclaimer policy to handle sponsored posts and links. For example http://www.moneysavingexpert.com/site/moneysavingexpert-finance is a very good example of how affiliated links are ethically handled as they state in the section of this page at "We want you to know when links are affiliated..."

Having specific two way guest blogging partnerships may help where you promote other bloggers and then they promote your services.

There are a number of blogger community sites, blog directories and pay for review sites you can use but make sure you have a process in place that will allow you to gain reviews on other websites ethically.

In terms of finding relevant bloggers to write about your services this can be done in a number of ways:

Social influencer research and direct outreach for which some useful tools are:
Buzzstream Discovery - https://idb.buzzstream.com - Social Influencer Discovery
Buzzsumo - https://app.buzzsumo.com/ - Content popularity and social influencer discovery
BuzzBundle - http://www.buzzbundle.com/ - Social Monitoring, Content Alerts and Influenecer Discovery
http://klear.com/free-tools - Find Influencers and analyze any social account across Twitter, Facebook and Instagram
https://www.hashatit.com/ - Find Twitter and Instagram influencers via Hashtag searches
http://followerwonk.com/ - Find and connect with new influencers in your niche
http://www.notey.com/ - Find specific content authors by country and theme
http://content.onalytica.com/ - Find influencers that fit your content
https://www.voilanorbert.com/ - Find an influencers email address

This method will require the most effort to engage in the social community but is likely to provide the best quality results

Blogger Marketplaces:
www.sponsoredreviews.com
https://izea.com/
http://www.contentfacilitator.com/
https://blogness.net/

Note: for all these you need to be very selective here to find the right blogs that will adhere to required standards

Use tools such as www.similarweb.com and Impactana content marketing Toolbar to estimate the readership and social popularity of any specific blog or post on a particular blog as this will help to use the right bloggers that will promote your services to the largest audience.

Blogger directories:
https://www.blogcatalog.com/
http://www.blogflux.com/
http://www.blogarama.com/
http://www.blogdigger.com/index.html

If you are based in the US or the UK you are more likely to find more suitable blog partners through these but if you are in another country you may want to do a more local search for country specific blog directories.

Blogger and Content communities:
It may be worth participating in a number of blogging communities to help find new prospects such as http://triberr.com/.

Another option may be to joing specific blogger and content groups on sites such as LinkedIn and Google +

It may even be worth checking out whether there are any local blogger meet up groups on meetup.com.